<?xml version="1.0" encoding="US-ASCII"?>
<!--XBRL Document Created with Wdesk from Workiva-->
<!-- -->
<link:linkbase xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <link:roleRef roleURI="http://www.aep.com/role/BenefitPlans" xlink:href="aep-20180331.xsd#BenefitPlans" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/BenefitPlansDetails" xlink:href="aep-20180331.xsd#BenefitPlansDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/BenefitPlansTables" xlink:href="aep-20180331.xsd#BenefitPlansTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/BusinessSegments" xlink:href="aep-20180331.xsd#BusinessSegments" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/BusinessSegmentsDetails" xlink:href="aep-20180331.xsd#BusinessSegmentsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/BusinessSegmentsTables" xlink:href="aep-20180331.xsd#BusinessSegmentsTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/CommitmentsGuaranteesAndContingencies" xlink:href="aep-20180331.xsd#CommitmentsGuaranteesAndContingencies" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/CommitmentsGuaranteesAndContingenciesDetails" xlink:href="aep-20180331.xsd#CommitmentsGuaranteesAndContingenciesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/CommitmentsGuaranteesAndContingenciesTables" xlink:href="aep-20180331.xsd#CommitmentsGuaranteesAndContingenciesTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/ComprehensiveIncome" xlink:href="aep-20180331.xsd#ComprehensiveIncome" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/ComprehensiveIncomeDetails" xlink:href="aep-20180331.xsd#ComprehensiveIncomeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/ComprehensiveIncomeTables" xlink:href="aep-20180331.xsd#ComprehensiveIncomeTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/CondensedConsolidatedBalanceSheets" xlink:href="aep-20180331.xsd#CondensedConsolidatedBalanceSheets" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/CondensedConsolidatedBalanceSheetsParenthetical" xlink:href="aep-20180331.xsd#CondensedConsolidatedBalanceSheetsParenthetical" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/CondensedConsolidatedStatementsOfCashFlows" xlink:href="aep-20180331.xsd#CondensedConsolidatedStatementsOfCashFlows" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/CondensedConsolidatedStatementsOfChangesInEquity" xlink:href="aep-20180331.xsd#CondensedConsolidatedStatementsOfChangesInEquity" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/ConsolidatedStatementsOfComprehensiveIncomeLoss" xlink:href="aep-20180331.xsd#ConsolidatedStatementsOfComprehensiveIncomeLoss" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/ConsolidatedStatementsOfComprehensiveIncomeLossParenthetical" xlink:href="aep-20180331.xsd#ConsolidatedStatementsOfComprehensiveIncomeLossParenthetical" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/ConsolidatedStatementsOfIncome" xlink:href="aep-20180331.xsd#ConsolidatedStatementsOfIncome" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/DerivativesAndHedging" xlink:href="aep-20180331.xsd#DerivativesAndHedging" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/DerivativesAndHedgingDetails" xlink:href="aep-20180331.xsd#DerivativesAndHedgingDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/DerivativesAndHedgingPolicies" xlink:href="aep-20180331.xsd#DerivativesAndHedgingPolicies" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/DerivativesAndHedgingTables" xlink:href="aep-20180331.xsd#DerivativesAndHedgingTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/DispositionsAndImpairments" xlink:href="aep-20180331.xsd#DispositionsAndImpairments" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/DispositionsAndImpairmentsDetails" xlink:href="aep-20180331.xsd#DispositionsAndImpairmentsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/DispositionsAndImpairmentsTables" xlink:href="aep-20180331.xsd#DispositionsAndImpairmentsTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/DocumentAndEntityInformation" xlink:href="aep-20180331.xsd#DocumentAndEntityInformation" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/FairValueAssetsAndLiabilitiesDetails" xlink:href="aep-20180331.xsd#FairValueAssetsAndLiabilitiesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/FairValueLongTermDebtOtherTemporaryInvestmentsNuclearTrustsDetails" xlink:href="aep-20180331.xsd#FairValueLongTermDebtOtherTemporaryInvestmentsNuclearTrustsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/FairValueMeasurements" xlink:href="aep-20180331.xsd#FairValueMeasurements" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/FairValueMeasurementsNucInvestmentsTextualsDetails" xlink:href="aep-20180331.xsd#FairValueMeasurementsNucInvestmentsTextualsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/FairValueMeasurementsPolicies" xlink:href="aep-20180331.xsd#FairValueMeasurementsPolicies" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/FairValueMeasurementsTables" xlink:href="aep-20180331.xsd#FairValueMeasurementsTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/FinancingActivities" xlink:href="aep-20180331.xsd#FinancingActivities" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/FinancingActivitiesDetails" xlink:href="aep-20180331.xsd#FinancingActivitiesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/FinancingActivitiesTables" xlink:href="aep-20180331.xsd#FinancingActivitiesTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/IncomeTaxes" xlink:href="aep-20180331.xsd#IncomeTaxes" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/IncomeTaxesDetails" xlink:href="aep-20180331.xsd#IncomeTaxesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/IncomeTaxesTables" xlink:href="aep-20180331.xsd#IncomeTaxesTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/NewAccountingPronouncements" xlink:href="aep-20180331.xsd#NewAccountingPronouncements" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/RateMatters" xlink:href="aep-20180331.xsd#RateMatters" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/RateMattersEastCompaniesDetails" xlink:href="aep-20180331.xsd#RateMattersEastCompaniesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/RateMattersRegulatoryAssetsDetails" xlink:href="aep-20180331.xsd#RateMattersRegulatoryAssetsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/RateMattersTables" xlink:href="aep-20180331.xsd#RateMattersTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/RateMattersWestCompaniesDetails" xlink:href="aep-20180331.xsd#RateMattersWestCompaniesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/RevenueFromContractsWithCustomersDetails" xlink:href="aep-20180331.xsd#RevenueFromContractsWithCustomersDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/RevenueFromContractsWithCustomersNotes" xlink:href="aep-20180331.xsd#RevenueFromContractsWithCustomersNotes" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/RevenueFromContractsWithCustomersPolicies" xlink:href="aep-20180331.xsd#RevenueFromContractsWithCustomersPolicies" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/RevenueFromContractsWithCustomersTables" xlink:href="aep-20180331.xsd#RevenueFromContractsWithCustomersTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/SignificantAccountingMatters" xlink:href="aep-20180331.xsd#SignificantAccountingMatters" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/SignificantAccountingMattersDetails" xlink:href="aep-20180331.xsd#SignificantAccountingMattersDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/SignificantAccountingMattersPolicies" xlink:href="aep-20180331.xsd#SignificantAccountingMattersPolicies" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/SignificantAccountingMattersTables" xlink:href="aep-20180331.xsd#SignificantAccountingMattersTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/VariableInterestEntitiesDetails" xlink:href="aep-20180331.xsd#VariableInterestEntitiesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/VariableInterestEntitiesNotes" xlink:href="aep-20180331.xsd#VariableInterestEntitiesNotes" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/VariableInterestEntitiesPolicies" xlink:href="aep-20180331.xsd#VariableInterestEntitiesPolicies" xlink:type="simple" />
  <link:roleRef roleURI="http://www.aep.com/role/VariableInterestEntitiesTables" xlink:href="aep-20180331.xsd#VariableInterestEntitiesTables" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" xlink:type="simple" />
  <link:definitionLink xlink:role="http://www.aep.com/role/BenefitPlans" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_B95BADC3D3D6342292DEFD0AEC453E98" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_BB8B9E8D40882298F2F9FD0AEC44920F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_B95BADC3D3D6342292DEFD0AEC453E98" xlink:to="loc_us-gaap_StatementTable_BB8B9E8D40882298F2F9FD0AEC44920F" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_4B3414A4AED35C9EC335FD0AEC449CFD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_BB8B9E8D40882298F2F9FD0AEC44920F" xlink:to="loc_dei_LegalEntityAxis_4B3414A4AED35C9EC335FD0AEC449CFD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_A789FE2EA5FA4FEB544EFD0AEC449B2B_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_4B3414A4AED35C9EC335FD0AEC449CFD" xlink:to="loc_dei_EntityDomain_A789FE2EA5FA4FEB544EFD0AEC449B2B_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_A789FE2EA5FA4FEB544EFD0AEC449B2B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_4B3414A4AED35C9EC335FD0AEC449CFD" xlink:to="loc_dei_EntityDomain_A789FE2EA5FA4FEB544EFD0AEC449B2B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock" xlink:label="loc_us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock_8E49C56C4652B6DC933AFD0AEC45A2D4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_B95BADC3D3D6342292DEFD0AEC453E98" xlink:to="loc_us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock_8E49C56C4652B6DC933AFD0AEC45A2D4" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/BenefitPlansDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_7D3CA149441882622D04D42FBF63E424" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_908B586232DA4EEC0CA7D42FBF63734F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_7D3CA149441882622D04D42FBF63E424" xlink:to="loc_us-gaap_StatementTable_908B586232DA4EEC0CA7D42FBF63734F" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RetirementPlanTypeAxis" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_607E6E6DDE51B07BA792D42FBF63272F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_908B586232DA4EEC0CA7D42FBF63734F" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_607E6E6DDE51B07BA792D42FBF63272F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RetirementPlanTypeDomain" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_1681EEDBEF4EE8B74FE3D42FBF634286_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_607E6E6DDE51B07BA792D42FBF63272F" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_1681EEDBEF4EE8B74FE3D42FBF634286_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RetirementPlanTypeDomain" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_1681EEDBEF4EE8B74FE3D42FBF634286" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_607E6E6DDE51B07BA792D42FBF63272F" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_1681EEDBEF4EE8B74FE3D42FBF634286" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PensionPlansDefinedBenefitMember" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_6EFCBB9E2DD3CA4A78AED42FBF635716" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_1681EEDBEF4EE8B74FE3D42FBF634286" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_6EFCBB9E2DD3CA4A78AED42FBF635716" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember" xlink:label="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_68F51E816F5BE83BC380D42FBF63DCEC" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_1681EEDBEF4EE8B74FE3D42FBF634286" xlink:to="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_68F51E816F5BE83BC380D42FBF63DCEC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_00EF5A3D138561051964D42FBF63733C" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_908B586232DA4EEC0CA7D42FBF63734F" xlink:to="loc_dei_LegalEntityAxis_00EF5A3D138561051964D42FBF63733C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_B07159FA5CD651128A8CD42FBF63432B_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_00EF5A3D138561051964D42FBF63733C" xlink:to="loc_dei_EntityDomain_B07159FA5CD651128A8CD42FBF63432B_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_B07159FA5CD651128A8CD42FBF63432B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_00EF5A3D138561051964D42FBF63733C" xlink:to="loc_dei_EntityDomain_B07159FA5CD651128A8CD42FBF63432B" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTexasInc.Member" xlink:label="loc_aep_AEPTexasInc.Member_35023AB89FA0B3D8286ED42FBF635D4A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_B07159FA5CD651128A8CD42FBF63432B" xlink:to="loc_aep_AEPTexasInc.Member_35023AB89FA0B3D8286ED42FBF635D4A" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AppalachianPowerCoMember" xlink:label="loc_aep_AppalachianPowerCoMember_05B13322C9492E549CA7D42FBF63A2F4" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_B07159FA5CD651128A8CD42FBF63432B" xlink:to="loc_aep_AppalachianPowerCoMember_05B13322C9492E549CA7D42FBF63A2F4" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IndianaMichiganPowerCoMember" xlink:label="loc_aep_IndianaMichiganPowerCoMember_737B3043FB2EB4B754B4D42FBF63EEDA" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_B07159FA5CD651128A8CD42FBF63432B" xlink:to="loc_aep_IndianaMichiganPowerCoMember_737B3043FB2EB4B754B4D42FBF63EEDA" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OhioPowerCoMember" xlink:label="loc_aep_OhioPowerCoMember_05FFE0DDFC7EC58677B6D42FBF63E2C0" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_B07159FA5CD651128A8CD42FBF63432B" xlink:to="loc_aep_OhioPowerCoMember_05FFE0DDFC7EC58677B6D42FBF63E2C0" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_PublicServiceCoOfOklahomaMember" xlink:label="loc_aep_PublicServiceCoOfOklahomaMember_F151F06C455D59B8F410D42FBF636D5D" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_B07159FA5CD651128A8CD42FBF63432B" xlink:to="loc_aep_PublicServiceCoOfOklahomaMember_F151F06C455D59B8F410D42FBF636D5D" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SouthwesternElectricPowerCoMember" xlink:label="loc_aep_SouthwesternElectricPowerCoMember_DDF5B29B144DCE20E305D42FBF631FED" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_B07159FA5CD651128A8CD42FBF63432B" xlink:to="loc_aep_SouthwesternElectricPowerCoMember_DDF5B29B144DCE20E305D42FBF631FED" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostAbstract" xlink:label="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostAbstract_9372A3075A9FD0CA7130D42FBF63AAA0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7D3CA149441882622D04D42FBF63E424" xlink:to="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostAbstract_9372A3075A9FD0CA7130D42FBF63AAA0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanServiceCost" xlink:label="loc_us-gaap_DefinedBenefitPlanServiceCost_DA848C6C9481C4AAB2F0D42FBF63DA26" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostAbstract_9372A3075A9FD0CA7130D42FBF63AAA0" xlink:to="loc_us-gaap_DefinedBenefitPlanServiceCost_DA848C6C9481C4AAB2F0D42FBF63DA26" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanInterestCost" xlink:label="loc_us-gaap_DefinedBenefitPlanInterestCost_925E242E5B3927421F7AD42FBF63B741" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostAbstract_9372A3075A9FD0CA7130D42FBF63AAA0" xlink:to="loc_us-gaap_DefinedBenefitPlanInterestCost_925E242E5B3927421F7AD42FBF63B741" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets_CE9713F2FE3C10344722D42FBF6300F8" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostAbstract_9372A3075A9FD0CA7130D42FBF63AAA0" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets_CE9713F2FE3C10344722D42FBF6300F8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit" xlink:label="loc_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit_D0E672895EB19264E336D42FBF63EF95" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostAbstract_9372A3075A9FD0CA7130D42FBF63AAA0" xlink:to="loc_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit_D0E672895EB19264E336D42FBF63EF95" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses" xlink:label="loc_us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses_2C6F7E3288EDFF509939D42FBF634141" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostAbstract_9372A3075A9FD0CA7130D42FBF63AAA0" xlink:to="loc_us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses_2C6F7E3288EDFF509939D42FBF634141" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost" xlink:label="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_7B87D9C4EB86147F8E08D42FBF635D1C" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostAbstract_9372A3075A9FD0CA7130D42FBF63AAA0" xlink:to="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_7B87D9C4EB86147F8E08D42FBF635D1C" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/BenefitPlansTables" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_B7DCD0873783D6CFFCA4FD0AEC402ABD" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_3BEA246971AD18004851FD0AEC3F78CE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_B7DCD0873783D6CFFCA4FD0AEC402ABD" xlink:to="loc_us-gaap_StatementTable_3BEA246971AD18004851FD0AEC3F78CE" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_3F5DBF0A4A3FFCADD3D3FD0AEC3FEE1D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_3BEA246971AD18004851FD0AEC3F78CE" xlink:to="loc_dei_LegalEntityAxis_3F5DBF0A4A3FFCADD3D3FD0AEC3FEE1D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_FAB9BA20C802578D8F25FD0AEC3F07E9_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_3F5DBF0A4A3FFCADD3D3FD0AEC3FEE1D" xlink:to="loc_dei_EntityDomain_FAB9BA20C802578D8F25FD0AEC3F07E9_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_FAB9BA20C802578D8F25FD0AEC3F07E9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_3F5DBF0A4A3FFCADD3D3FD0AEC3FEE1D" xlink:to="loc_dei_EntityDomain_FAB9BA20C802578D8F25FD0AEC3F07E9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfNetBenefitCostsTableTextBlock" xlink:label="loc_us-gaap_ScheduleOfNetBenefitCostsTableTextBlock_CEBD4FEF2A4948CC3178FD0AEC4055A4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_B7DCD0873783D6CFFCA4FD0AEC402ABD" xlink:to="loc_us-gaap_ScheduleOfNetBenefitCostsTableTextBlock_CEBD4FEF2A4948CC3178FD0AEC4055A4" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/BusinessSegments" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_75FC99F7489EFD695992877628301573" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_6792CD57097EA1AE035D877628208F1F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_75FC99F7489EFD695992877628301573" xlink:to="loc_us-gaap_StatementTable_6792CD57097EA1AE035D877628208F1F" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_10BEA7958824DA55BE1687762830D0EC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_6792CD57097EA1AE035D877628208F1F" xlink:to="loc_dei_LegalEntityAxis_10BEA7958824DA55BE1687762830D0EC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_4AF4C52C5DBEB3D5A0FA877628300515_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_10BEA7958824DA55BE1687762830D0EC" xlink:to="loc_dei_EntityDomain_4AF4C52C5DBEB3D5A0FA877628300515_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_4AF4C52C5DBEB3D5A0FA877628300515" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_10BEA7958824DA55BE1687762830D0EC" xlink:to="loc_dei_EntityDomain_4AF4C52C5DBEB3D5A0FA877628300515" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentReportingDisclosureTextBlock" xlink:label="loc_us-gaap_SegmentReportingDisclosureTextBlock_D4D4228FB0DF880EBFBF87762830659E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_75FC99F7489EFD695992877628301573" xlink:to="loc_us-gaap_SegmentReportingDisclosureTextBlock_D4D4228FB0DF880EBFBF87762830659E" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/BusinessSegmentsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_CC51BEA3C9D20608AA60FCBE3EA39E82" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_377B5CE626FF9F3963F4FCBE3EA2AC82" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_CC51BEA3C9D20608AA60FCBE3EA39E82" xlink:to="loc_us-gaap_StatementTable_377B5CE626FF9F3963F4FCBE3EA2AC82" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_8399DF5B9ECDCF983FC0FCBE3EA2115B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_377B5CE626FF9F3963F4FCBE3EA2AC82" xlink:to="loc_dei_LegalEntityAxis_8399DF5B9ECDCF983FC0FCBE3EA2115B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_405EC8A97338FB54A538FCBE3EA2A0DB_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_8399DF5B9ECDCF983FC0FCBE3EA2115B" xlink:to="loc_dei_EntityDomain_405EC8A97338FB54A538FCBE3EA2A0DB_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_405EC8A97338FB54A538FCBE3EA2A0DB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_8399DF5B9ECDCF983FC0FCBE3EA2115B" xlink:to="loc_dei_EntityDomain_405EC8A97338FB54A538FCBE3EA2A0DB" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTransmissionCoMember" xlink:label="loc_aep_AEPTransmissionCoMember_C3B6191A55108F424583FCBE3EA24DE9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_405EC8A97338FB54A538FCBE3EA2A0DB" xlink:to="loc_aep_AEPTransmissionCoMember_C3B6191A55108F424583FCBE3EA24DE9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationItemsAxis" xlink:label="loc_us-gaap_ConsolidationItemsAxis_3A25F59D793A5B4A6BF8FCBE3EA3EEF9" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_377B5CE626FF9F3963F4FCBE3EA2AC82" xlink:to="loc_us-gaap_ConsolidationItemsAxis_3A25F59D793A5B4A6BF8FCBE3EA3EEF9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationItemsDomain" xlink:label="loc_us-gaap_ConsolidationItemsDomain_CCE685F42384525D6CFDFCBE3EA3130B_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConsolidationItemsAxis_3A25F59D793A5B4A6BF8FCBE3EA3EEF9" xlink:to="loc_us-gaap_ConsolidationItemsDomain_CCE685F42384525D6CFDFCBE3EA3130B_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationItemsDomain" xlink:label="loc_us-gaap_ConsolidationItemsDomain_CCE685F42384525D6CFDFCBE3EA3130B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConsolidationItemsAxis_3A25F59D793A5B4A6BF8FCBE3EA3EEF9" xlink:to="loc_us-gaap_ConsolidationItemsDomain_CCE685F42384525D6CFDFCBE3EA3130B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationEliminationsMember" xlink:label="loc_us-gaap_ConsolidationEliminationsMember_FDDC06EB450EB5FDAC4DFCBE3EA32EF6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidationItemsDomain_CCE685F42384525D6CFDFCBE3EA3130B" xlink:to="loc_us-gaap_ConsolidationEliminationsMember_FDDC06EB450EB5FDAC4DFCBE3EA32EF6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_4BF05669BB3C87E9D40DFCBE3EA31A72" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_377B5CE626FF9F3963F4FCBE3EA2AC82" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_4BF05669BB3C87E9D40DFCBE3EA31A72" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_EAC78E1D18F15679F37FFCBE3EA3B91F_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_4BF05669BB3C87E9D40DFCBE3EA31A72" xlink:to="loc_us-gaap_SegmentDomain_EAC78E1D18F15679F37FFCBE3EA3B91F_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_EAC78E1D18F15679F37FFCBE3EA3B91F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_4BF05669BB3C87E9D40DFCBE3EA31A72" xlink:to="loc_us-gaap_SegmentDomain_EAC78E1D18F15679F37FFCBE3EA3B91F" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_VerticallyIntegratedUtilitiesMember" xlink:label="loc_aep_VerticallyIntegratedUtilitiesMember_0FF1B9C952AF96E50811FCBE3EA31AB4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_EAC78E1D18F15679F37FFCBE3EA3B91F" xlink:to="loc_aep_VerticallyIntegratedUtilitiesMember_0FF1B9C952AF96E50811FCBE3EA31AB4" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_TransmissionAndDistributionCompaniesMember" xlink:label="loc_aep_TransmissionAndDistributionCompaniesMember_72F8B21044C9F66952FBFCBE3EA334C1" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_EAC78E1D18F15679F37FFCBE3EA3B91F" xlink:to="loc_aep_TransmissionAndDistributionCompaniesMember_72F8B21044C9F66952FBFCBE3EA334C1" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTransmissionHoldcoMember" xlink:label="loc_aep_AEPTransmissionHoldcoMember_E1936B623BFB7781650DFCBE3EA3DC74" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_EAC78E1D18F15679F37FFCBE3EA3B91F" xlink:to="loc_aep_AEPTransmissionHoldcoMember_E1936B623BFB7781650DFCBE3EA3DC74" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_GenerationAndMarketingMember" xlink:label="loc_aep_GenerationAndMarketingMember_1C9B2E5921B5725BC9CBFCBE3EA3F4BA" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_EAC78E1D18F15679F37FFCBE3EA3B91F" xlink:to="loc_aep_GenerationAndMarketingMember_1C9B2E5921B5725BC9CBFCBE3EA3F4BA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AllOtherSegmentsMember" xlink:label="loc_us-gaap_AllOtherSegmentsMember_0750C07BF58ED59EDB6DFCBE3EA3DB92" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_EAC78E1D18F15679F37FFCBE3EA3B91F" xlink:to="loc_us-gaap_AllOtherSegmentsMember_0750C07BF58ED59EDB6DFCBE3EA3DB92" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_StateTranscosMember" xlink:label="loc_aep_StateTranscosMember_0EF33D656CA1E0808D8DFCBE3EA38035" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_EAC78E1D18F15679F37FFCBE3EA3B91F" xlink:to="loc_aep_StateTranscosMember_0EF33D656CA1E0808D8DFCBE3EA38035" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTCoParentMember" xlink:label="loc_aep_AEPTCoParentMember_08607CCFD48E3D7DC486FCBE3EA336BA" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_EAC78E1D18F15679F37FFCBE3EA3B91F" xlink:to="loc_aep_AEPTCoParentMember_08607CCFD48E3D7DC486FCBE3EA336BA" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTransmissionCoMember" xlink:label="loc_aep_AEPTransmissionCoMember_F32505B54639D426FB91FCBE3EA3A11F" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_EAC78E1D18F15679F37FFCBE3EA3B91F" xlink:to="loc_aep_AEPTransmissionCoMember_F32505B54639D426FB91FCBE3EA3A11F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentReportingInformationProfitLossAbstract" xlink:label="loc_us-gaap_SegmentReportingInformationProfitLossAbstract_7A00F703BA7D95EA2179FCBE3EA481D0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_CC51BEA3C9D20608AA60FCBE3EA39E82" xlink:to="loc_us-gaap_SegmentReportingInformationProfitLossAbstract_7A00F703BA7D95EA2179FCBE3EA481D0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ElectricUtilityRevenue" xlink:label="loc_us-gaap_ElectricUtilityRevenue_C3C05865569D4F507C2DFCBE3EA4BE3F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationProfitLossAbstract_7A00F703BA7D95EA2179FCBE3EA481D0" xlink:to="loc_us-gaap_ElectricUtilityRevenue_C3C05865569D4F507C2DFCBE3EA4BE3F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ElectricalTransmissionAndDistributionRevenue" xlink:label="loc_us-gaap_ElectricalTransmissionAndDistributionRevenue_568FCA6A86375C85AC27FCBE3EA41A8D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationProfitLossAbstract_7A00F703BA7D95EA2179FCBE3EA481D0" xlink:to="loc_us-gaap_ElectricalTransmissionAndDistributionRevenue_568FCA6A86375C85AC27FCBE3EA41A8D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ElectricalTransmissionRevenue" xlink:label="loc_us-gaap_ElectricalTransmissionRevenue_473AF889DA66DA1EE6DCFCBE3EA4F395" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationProfitLossAbstract_7A00F703BA7D95EA2179FCBE3EA481D0" xlink:to="loc_us-gaap_ElectricalTransmissionRevenue_473AF889DA66DA1EE6DCFCBE3EA4F395" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ElectricalGenerationRevenue" xlink:label="loc_us-gaap_ElectricalGenerationRevenue_292927421A1B679A3CF1FCBE3EA43F00" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationProfitLossAbstract_7A00F703BA7D95EA2179FCBE3EA481D0" xlink:to="loc_us-gaap_ElectricalGenerationRevenue_292927421A1B679A3CF1FCBE3EA43F00" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RevenueFromRelatedParties" xlink:label="loc_us-gaap_RevenueFromRelatedParties_5466FA24A406D660D5CEFCBE3EA42D8A" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationProfitLossAbstract_7A00F703BA7D95EA2179FCBE3EA481D0" xlink:to="loc_us-gaap_RevenueFromRelatedParties_5466FA24A406D660D5CEFCBE3EA42D8A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherSalesRevenueNet" xlink:label="loc_us-gaap_OtherSalesRevenueNet_D2D6B7B8B2963E6A99CBFCBE3EA42E59" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationProfitLossAbstract_7A00F703BA7D95EA2179FCBE3EA481D0" xlink:to="loc_us-gaap_OtherSalesRevenueNet_D2D6B7B8B2963E6A99CBFCBE3EA42E59" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Revenues" xlink:label="loc_us-gaap_Revenues_63EBD42B26A1288298A4FCBE3EA4DF88" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationProfitLossAbstract_7A00F703BA7D95EA2179FCBE3EA481D0" xlink:to="loc_us-gaap_Revenues_63EBD42B26A1288298A4FCBE3EA4DF88" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentIncomeInterestAndDividend" xlink:label="loc_us-gaap_InvestmentIncomeInterestAndDividend_B8681EAD69832D960A79FCBE3EA43BBD" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationProfitLossAbstract_7A00F703BA7D95EA2179FCBE3EA481D0" xlink:to="loc_us-gaap_InvestmentIncomeInterestAndDividend_B8681EAD69832D960A79FCBE3EA43BBD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InterestExpense" xlink:label="loc_us-gaap_InterestExpense_E5B72EB18FB263C6C76FFCBE3EA4B8DC" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationProfitLossAbstract_7A00F703BA7D95EA2179FCBE3EA481D0" xlink:to="loc_us-gaap_InterestExpense_E5B72EB18FB263C6C76FFCBE3EA4B8DC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_4877C143F388A6473D9AFCBE3EA49108" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationProfitLossAbstract_7A00F703BA7D95EA2179FCBE3EA481D0" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_4877C143F388A6473D9AFCBE3EA49108" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProfitLoss" xlink:label="loc_us-gaap_ProfitLoss_8C443FF8843149D03069FCBE3EA4D723" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationProfitLossAbstract_7A00F703BA7D95EA2179FCBE3EA481D0" xlink:to="loc_us-gaap_ProfitLoss_8C443FF8843149D03069FCBE3EA4D723" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentReportingInformationAdditionalInformationAbstract" xlink:label="loc_us-gaap_SegmentReportingInformationAdditionalInformationAbstract_53D490337B57D5B2DD9DFCBE3EA4D92E" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_CC51BEA3C9D20608AA60FCBE3EA39E82" xlink:to="loc_us-gaap_SegmentReportingInformationAdditionalInformationAbstract_53D490337B57D5B2DD9DFCBE3EA4D92E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentGross" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_C66F7B51FF47C52F025EFCBE3EA597B1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationAdditionalInformationAbstract_53D490337B57D5B2DD9DFCBE3EA4D92E" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_C66F7B51FF47C52F025EFCBE3EA597B1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_76E0A6A6E9426E66D63CFCBE3EA525DA" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationAdditionalInformationAbstract_53D490337B57D5B2DD9DFCBE3EA4D92E" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_76E0A6A6E9426E66D63CFCBE3EA525DA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_A24E96C5A321FB605EBBFCBE3EA59106" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationAdditionalInformationAbstract_53D490337B57D5B2DD9DFCBE3EA4D92E" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_A24E96C5A321FB605EBBFCBE3EA59106" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NotesReceivableRelatedParties" xlink:label="loc_us-gaap_NotesReceivableRelatedParties_BAA35609F4EAC85FE8A0FCBE3EA59679" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationAdditionalInformationAbstract_53D490337B57D5B2DD9DFCBE3EA4D92E" xlink:to="loc_us-gaap_NotesReceivableRelatedParties_BAA35609F4EAC85FE8A0FCBE3EA59679" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Assets" xlink:label="loc_us-gaap_Assets_7758F42C6BF5D6CB0361FCBE3EA56A17" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationAdditionalInformationAbstract_53D490337B57D5B2DD9DFCBE3EA4D92E" xlink:to="loc_us-gaap_Assets_7758F42C6BF5D6CB0361FCBE3EA56A17" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermDebtCurrent" xlink:label="loc_us-gaap_LongTermDebtCurrent_5FA8C2EE4E8871E96597FCBE3EA5B52C" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationAdditionalInformationAbstract_53D490337B57D5B2DD9DFCBE3EA4D92E" xlink:to="loc_us-gaap_LongTermDebtCurrent_5FA8C2EE4E8871E96597FCBE3EA5B52C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AffiliatedLongTermDebtNoncurrent" xlink:label="loc_aep_AffiliatedLongTermDebtNoncurrent_C67C90DB657DC9F2DB76FCBE3EA56C54" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationAdditionalInformationAbstract_53D490337B57D5B2DD9DFCBE3EA4D92E" xlink:to="loc_aep_AffiliatedLongTermDebtNoncurrent_C67C90DB657DC9F2DB76FCBE3EA56C54" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermDebtNoncurrent" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_9DD8750DEA8620378944FCBE3EA52F61" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationAdditionalInformationAbstract_53D490337B57D5B2DD9DFCBE3EA4D92E" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_9DD8750DEA8620378944FCBE3EA52F61" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermDebt" xlink:label="loc_us-gaap_LongTermDebt_654743B4FDD68C02C2A2FCBE3EA5A24A" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationAdditionalInformationAbstract_53D490337B57D5B2DD9DFCBE3EA4D92E" xlink:to="loc_us-gaap_LongTermDebt_654743B4FDD68C02C2A2FCBE3EA5A24A" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/BusinessSegmentsTables" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_78ACDC26C56215FFB05E8778AD7C20AC" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_E1AB3ABBA075BBD046948778AD7CEE13" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_78ACDC26C56215FFB05E8778AD7C20AC" xlink:to="loc_us-gaap_StatementTable_E1AB3ABBA075BBD046948778AD7CEE13" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_C9B680D249C6B6B675B287798E6F3A8F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_E1AB3ABBA075BBD046948778AD7CEE13" xlink:to="loc_dei_LegalEntityAxis_C9B680D249C6B6B675B287798E6F3A8F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_90C99C031C1C6E285C1D87798FBA327B_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_C9B680D249C6B6B675B287798E6F3A8F" xlink:to="loc_dei_EntityDomain_90C99C031C1C6E285C1D87798FBA327B_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_90C99C031C1C6E285C1D87798FBA327B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_C9B680D249C6B6B675B287798E6F3A8F" xlink:to="loc_dei_EntityDomain_90C99C031C1C6E285C1D87798FBA327B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTextBlock" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTextBlock_F589521DC4FF720E6DC98778646C2D2B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_78ACDC26C56215FFB05E8778AD7C20AC" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTextBlock_F589521DC4FF720E6DC98778646C2D2B" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/CommitmentsGuaranteesAndContingencies" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_87C8450715AF3B11826FFD0AEC6E45E2" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_CD92D52F3673C78A3C5FFD0AEC6E5A94" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_87C8450715AF3B11826FFD0AEC6E45E2" xlink:to="loc_us-gaap_StatementTable_CD92D52F3673C78A3C5FFD0AEC6E5A94" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_D235A9D432E5475A1143FD0AEC6E5F94" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_CD92D52F3673C78A3C5FFD0AEC6E5A94" xlink:to="loc_dei_LegalEntityAxis_D235A9D432E5475A1143FD0AEC6E5F94" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_21DC3775FEC64A2240ECFD0AEC6E4627_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_D235A9D432E5475A1143FD0AEC6E5F94" xlink:to="loc_dei_EntityDomain_21DC3775FEC64A2240ECFD0AEC6E4627_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_21DC3775FEC64A2240ECFD0AEC6E4627" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_D235A9D432E5475A1143FD0AEC6E5F94" xlink:to="loc_dei_EntityDomain_21DC3775FEC64A2240ECFD0AEC6E4627" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommitmentsContingenciesAndGuaranteesTextBlock" xlink:label="loc_us-gaap_CommitmentsContingenciesAndGuaranteesTextBlock_E83B35C4C9CC6690338AFD0AEC6E0E3B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_87C8450715AF3B11826FFD0AEC6E45E2" xlink:to="loc_us-gaap_CommitmentsContingenciesAndGuaranteesTextBlock_E83B35C4C9CC6690338AFD0AEC6E0E3B" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/CommitmentsGuaranteesAndContingenciesDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_0D7B4A7EC38C59B4636EF92C29EA1AF9" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_43E96DA851F436F59D60F92C29E8FC16" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_0D7B4A7EC38C59B4636EF92C29EA1AF9" xlink:to="loc_us-gaap_StatementTable_43E96DA851F436F59D60F92C29E8FC16" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaturityofCreditFacilityAxis" xlink:label="loc_aep_MaturityofCreditFacilityAxis_D0370C507B2D7B2356ECF92C29E86B5B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_43E96DA851F436F59D60F92C29E8FC16" xlink:to="loc_aep_MaturityofCreditFacilityAxis_D0370C507B2D7B2356ECF92C29E86B5B" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaturityofcreditfacilityDomain" xlink:label="loc_aep_MaturityofcreditfacilityDomain_08C2A4F9743E12CF7DD2F92C29E8D83D_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_aep_MaturityofCreditFacilityAxis_D0370C507B2D7B2356ECF92C29E86B5B" xlink:to="loc_aep_MaturityofcreditfacilityDomain_08C2A4F9743E12CF7DD2F92C29E8D83D_default" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaturityofcreditfacilityDomain" xlink:label="loc_aep_MaturityofcreditfacilityDomain_08C2A4F9743E12CF7DD2F92C29E8D83D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_aep_MaturityofCreditFacilityAxis_D0370C507B2D7B2356ECF92C29E86B5B" xlink:to="loc_aep_MaturityofcreditfacilityDomain_08C2A4F9743E12CF7DD2F92C29E8D83D" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_June2021Member" xlink:label="loc_aep_June2021Member_87185ACDC98E0CD4B57EF92C29E8FA50" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_MaturityofcreditfacilityDomain_08C2A4F9743E12CF7DD2F92C29E8D83D" xlink:to="loc_aep_June2021Member_87185ACDC98E0CD4B57EF92C29E8FA50" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_July2019Member" xlink:label="loc_aep_July2019Member_AEEE2C8D6B7313074C0FF92C29E8B819" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_MaturityofcreditfacilityDomain_08C2A4F9743E12CF7DD2F92C29E8D83D" xlink:to="loc_aep_July2019Member_AEEE2C8D6B7313074C0FF92C29E8B819" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MajorPropertyClassAxis" xlink:label="loc_us-gaap_MajorPropertyClassAxis_E3A331C5DBA980B6DF9CF92C29E93056" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_43E96DA851F436F59D60F92C29E8FC16" xlink:to="loc_us-gaap_MajorPropertyClassAxis_E3A331C5DBA980B6DF9CF92C29E93056" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MajorPropertyClassDomain" xlink:label="loc_us-gaap_MajorPropertyClassDomain_90A45194AFDA2E578B75F92C29E9F289_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MajorPropertyClassAxis_E3A331C5DBA980B6DF9CF92C29E93056" xlink:to="loc_us-gaap_MajorPropertyClassDomain_90A45194AFDA2E578B75F92C29E9F289_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MajorPropertyClassDomain" xlink:label="loc_us-gaap_MajorPropertyClassDomain_90A45194AFDA2E578B75F92C29E9F289" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MajorPropertyClassAxis_E3A331C5DBA980B6DF9CF92C29E93056" xlink:to="loc_us-gaap_MajorPropertyClassDomain_90A45194AFDA2E578B75F92C29E9F289" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RailcarLeaseMember" xlink:label="loc_aep_RailcarLeaseMember_A590E45F46D7EB3DD3B0F92C29E93F5F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorPropertyClassDomain_90A45194AFDA2E578B75F92C29E9F289" xlink:to="loc_aep_RailcarLeaseMember_A590E45F46D7EB3DD3B0F92C29E93F5F" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_BoatandBargeLeasesMember" xlink:label="loc_aep_BoatandBargeLeasesMember_5D6A825CEF339C5492F5F92C29E9EB03" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorPropertyClassDomain_90A45194AFDA2E578B75F92C29E9F289" xlink:to="loc_aep_BoatandBargeLeasesMember_5D6A825CEF339C5492F5F92C29E9EB03" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_6BBA61EF19EA62570A71F92C29E9FCD0" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_43E96DA851F436F59D60F92C29E8FC16" xlink:to="loc_dei_LegalEntityAxis_6BBA61EF19EA62570A71F92C29E9FCD0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_2C9B4116C2484EAE77FCF92C29E94ED4_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_6BBA61EF19EA62570A71F92C29E9FCD0" xlink:to="loc_dei_EntityDomain_2C9B4116C2484EAE77FCF92C29E94ED4_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_2C9B4116C2484EAE77FCF92C29E94ED4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_6BBA61EF19EA62570A71F92C29E9FCD0" xlink:to="loc_dei_EntityDomain_2C9B4116C2484EAE77FCF92C29E94ED4" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTexasInc.Member" xlink:label="loc_aep_AEPTexasInc.Member_132D9E82F7B8ED76018CF92C29E9D7A8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_2C9B4116C2484EAE77FCF92C29E94ED4" xlink:to="loc_aep_AEPTexasInc.Member_132D9E82F7B8ED76018CF92C29E9D7A8" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTransmissionCoMember" xlink:label="loc_aep_AEPTransmissionCoMember_8A187FB7939C98C47A33F92C29E9F634" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_2C9B4116C2484EAE77FCF92C29E94ED4" xlink:to="loc_aep_AEPTransmissionCoMember_8A187FB7939C98C47A33F92C29E9F634" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AppalachianPowerCoMember" xlink:label="loc_aep_AppalachianPowerCoMember_A4556743500EEE969861F92C29E934A1" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_2C9B4116C2484EAE77FCF92C29E94ED4" xlink:to="loc_aep_AppalachianPowerCoMember_A4556743500EEE969861F92C29E934A1" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IndianaMichiganPowerCoMember" xlink:label="loc_aep_IndianaMichiganPowerCoMember_C2126F3317E7964AFC6DF92C29EA0D0A" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_2C9B4116C2484EAE77FCF92C29E94ED4" xlink:to="loc_aep_IndianaMichiganPowerCoMember_C2126F3317E7964AFC6DF92C29EA0D0A" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OhioPowerCoMember" xlink:label="loc_aep_OhioPowerCoMember_D45DD094E74D23C8F5E5F92C29EAF560" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_2C9B4116C2484EAE77FCF92C29E94ED4" xlink:to="loc_aep_OhioPowerCoMember_D45DD094E74D23C8F5E5F92C29EAF560" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_PublicServiceCoOfOklahomaMember" xlink:label="loc_aep_PublicServiceCoOfOklahomaMember_9D0AB370B89FE48E4F0DF92C29EAD736" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_2C9B4116C2484EAE77FCF92C29E94ED4" xlink:to="loc_aep_PublicServiceCoOfOklahomaMember_9D0AB370B89FE48E4F0DF92C29EAD736" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SouthwesternElectricPowerCoMember" xlink:label="loc_aep_SouthwesternElectricPowerCoMember_B7D440132579DACB672EF92C29EAAC42" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_2C9B4116C2484EAE77FCF92C29E94ED4" xlink:to="loc_aep_SouthwesternElectricPowerCoMember_B7D440132579DACB672EF92C29EAAC42" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GuaranteeObligationsByNatureAxis" xlink:label="loc_us-gaap_GuaranteeObligationsByNatureAxis_7D87AB20406AEAD4BB18F92C29EA3297" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_43E96DA851F436F59D60F92C29E8FC16" xlink:to="loc_us-gaap_GuaranteeObligationsByNatureAxis_7D87AB20406AEAD4BB18F92C29EA3297" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GuaranteeObligationsNatureDomain" xlink:label="loc_us-gaap_GuaranteeObligationsNatureDomain_3BA594D28D6EE4D1B955F92C29EA45B2_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_GuaranteeObligationsByNatureAxis_7D87AB20406AEAD4BB18F92C29EA3297" xlink:to="loc_us-gaap_GuaranteeObligationsNatureDomain_3BA594D28D6EE4D1B955F92C29EA45B2_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GuaranteeObligationsNatureDomain" xlink:label="loc_us-gaap_GuaranteeObligationsNatureDomain_3BA594D28D6EE4D1B955F92C29EA45B2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_GuaranteeObligationsByNatureAxis_7D87AB20406AEAD4BB18F92C29EA3297" xlink:to="loc_us-gaap_GuaranteeObligationsNatureDomain_3BA594D28D6EE4D1B955F92C29EA45B2" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_LettersOfCreditMember" xlink:label="loc_aep_LettersOfCreditMember_831EDBEED2177829F52DF92C29EA11AA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GuaranteeObligationsNatureDomain_3BA594D28D6EE4D1B955F92C29EA45B2" xlink:to="loc_aep_LettersOfCreditMember_831EDBEED2177829F52DF92C29EA11AA" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_GuaranteesOfThirdPartyObligationsMember" xlink:label="loc_aep_GuaranteesOfThirdPartyObligationsMember_83833DC2F22EA42D2667F92C29EA2F7B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GuaranteeObligationsNatureDomain_3BA594D28D6EE4D1B955F92C29EA45B2" xlink:to="loc_aep_GuaranteesOfThirdPartyObligationsMember_83833DC2F22EA42D2667F92C29EA2F7B" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_GuaranteesofEquityMethodInvesteesMember" xlink:label="loc_aep_GuaranteesofEquityMethodInvesteesMember_D7B115FA4712DA5B543CF92C29EA31CB" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GuaranteeObligationsNatureDomain_3BA594D28D6EE4D1B955F92C29EA45B2" xlink:to="loc_aep_GuaranteesofEquityMethodInvesteesMember_D7B115FA4712DA5B543CF92C29EA31CB" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MasterLeaseAgreementsMember" xlink:label="loc_aep_MasterLeaseAgreementsMember_60E5115D7A3D69A7E5BBF92C29EA0BD1" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GuaranteeObligationsNatureDomain_3BA594D28D6EE4D1B955F92C29EA45B2" xlink:to="loc_aep_MasterLeaseAgreementsMember_60E5115D7A3D69A7E5BBF92C29EA0BD1" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaximumFuturePaymentsforLettersofCreditUnderUncommittedFacilitiesAbstract" xlink:label="loc_aep_MaximumFuturePaymentsforLettersofCreditUnderUncommittedFacilitiesAbstract_5586F4930660D1DE1947F92C29EA3893" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_0D7B4A7EC38C59B4636EF92C29EA1AF9" xlink:to="loc_aep_MaximumFuturePaymentsforLettersofCreditUnderUncommittedFacilitiesAbstract_5586F4930660D1DE1947F92C29EA3893" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaximumFuturePaymentsforLettersofCreditIssuedUndertheUncommittedFacility" xlink:label="loc_aep_MaximumFuturePaymentsforLettersofCreditIssuedUndertheUncommittedFacility_641447E43D079D17AC20F92C29EA70B2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_MaximumFuturePaymentsforLettersofCreditUnderUncommittedFacilitiesAbstract_5586F4930660D1DE1947F92C29EA3893" xlink:to="loc_aep_MaximumFuturePaymentsforLettersofCreditIssuedUndertheUncommittedFacility_641447E43D079D17AC20F92C29EA70B2" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaximumPotentialLossOnMasterLeaseAgreementsAbstract" xlink:label="loc_aep_MaximumPotentialLossOnMasterLeaseAgreementsAbstract_9AF01DB72A678546CC38F92C29EACFCE" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_0D7B4A7EC38C59B4636EF92C29EA1AF9" xlink:to="loc_aep_MaximumPotentialLossOnMasterLeaseAgreementsAbstract_9AF01DB72A678546CC38F92C29EACFCE" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaxPotentialLossOnMasterLeaseAgreements" xlink:label="loc_aep_MaxPotentialLossOnMasterLeaseAgreements_DF645D5885C4BD05D6C8F92C29EA5A5C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_MaximumPotentialLossOnMasterLeaseAgreementsAbstract_9AF01DB72A678546CC38F92C29EACFCE" xlink:to="loc_aep_MaxPotentialLossOnMasterLeaseAgreements_DF645D5885C4BD05D6C8F92C29EA5A5C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_CommitmentsGuaranteesAndContingenciesTextualsAbstract" xlink:label="loc_aep_CommitmentsGuaranteesAndContingenciesTextualsAbstract_D306F600406F87096F3CF92C29EBD497" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_0D7B4A7EC38C59B4636EF92C29EA1AF9" xlink:to="loc_aep_CommitmentsGuaranteesAndContingenciesTextualsAbstract_D306F600406F87096F3CF92C29EBD497" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_CreditFacilitiesStructured" xlink:label="loc_aep_CreditFacilitiesStructured_DD719FCEC3615EA1D257F92C29EB1EFC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CommitmentsGuaranteesAndContingenciesTextualsAbstract_D306F600406F87096F3CF92C29EBD497" xlink:to="loc_aep_CreditFacilitiesStructured_DD719FCEC3615EA1D257F92C29EB1EFC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_541DF10569674AECD48AF92C29EBE5B6" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CommitmentsGuaranteesAndContingenciesTextualsAbstract_D306F600406F87096F3CF92C29EBD497" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_541DF10569674AECD48AF92C29EBE5B6" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_UncommittedFacility" xlink:label="loc_aep_UncommittedFacility_C19127EFCBB561EF4A9CF92C29EB2890" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CommitmentsGuaranteesAndContingenciesTextualsAbstract_D306F600406F87096F3CF92C29EBD497" xlink:to="loc_aep_UncommittedFacility_C19127EFCBB561EF4A9CF92C29EB2890" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_DecreasedUncommittedFacility" xlink:label="loc_aep_DecreasedUncommittedFacility_4A9B23A8B9D90A594B79F92C29EBB3F3" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CommitmentsGuaranteesAndContingenciesTextualsAbstract_D306F600406F87096F3CF92C29EBD497" xlink:to="loc_aep_DecreasedUncommittedFacility_4A9B23A8B9D90A594B79F92C29EBB3F3" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_VariableRatePcbsSupported" xlink:label="loc_aep_VariableRatePcbsSupported_3E059DE6A7E8D785B2DAF92C29EBC85C" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CommitmentsGuaranteesAndContingenciesTextualsAbstract_D306F600406F87096F3CF92C29EBD497" xlink:to="loc_aep_VariableRatePcbsSupported_3E059DE6A7E8D785B2DAF92C29EBC85C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LettersOfCreditOutstandingAmount" xlink:label="loc_us-gaap_LettersOfCreditOutstandingAmount_D05CE97F65BF2613CAD6F92C29EB3F38" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CommitmentsGuaranteesAndContingenciesTextualsAbstract_D306F600406F87096F3CF92C29EBD497" xlink:to="loc_us-gaap_LettersOfCreditOutstandingAmount_D05CE97F65BF2613CAD6F92C29EB3F38" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_GuaranteesOfMineReclamationAmount" xlink:label="loc_aep_GuaranteesOfMineReclamationAmount_A30A97557ED431F61388F92C29EBC91C" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CommitmentsGuaranteesAndContingenciesTextualsAbstract_D306F600406F87096F3CF92C29EBD497" xlink:to="loc_aep_GuaranteesOfMineReclamationAmount_A30A97557ED431F61388F92C29EBC91C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MineReclamationAndClosingLiabilityNoncurrent" xlink:label="loc_us-gaap_MineReclamationAndClosingLiabilityNoncurrent_C73100ED63A7E00858E5F92C29EB1940" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CommitmentsGuaranteesAndContingenciesTextualsAbstract_D306F600406F87096F3CF92C29EBD497" xlink:to="loc_us-gaap_MineReclamationAndClosingLiabilityNoncurrent_C73100ED63A7E00858E5F92C29EB1940" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AmountCollectedThroughRiderForFinalMineClosureAndReclamationCosts" xlink:label="loc_aep_AmountCollectedThroughRiderForFinalMineClosureAndReclamationCosts_4B5280181BAC2D17F2C0F92C29EBDDCF" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CommitmentsGuaranteesAndContingenciesTextualsAbstract_D306F600406F87096F3CF92C29EBD497" xlink:to="loc_aep_AmountCollectedThroughRiderForFinalMineClosureAndReclamationCosts_4B5280181BAC2D17F2C0F92C29EBDDCF" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AmountCollectedRiderMineCloseAroNoncurrent" xlink:label="loc_aep_AmountCollectedRiderMineCloseAroNoncurrent_4A176FF558C1F2FFA951F92C29EBD5A0" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CommitmentsGuaranteesAndContingenciesTextualsAbstract_D306F600406F87096F3CF92C29EBD497" xlink:to="loc_aep_AmountCollectedRiderMineCloseAroNoncurrent_4A176FF558C1F2FFA951F92C29EBD5A0" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AmountCollectedRiderMineCloseOtherAssetsNoncurrent" xlink:label="loc_aep_AmountCollectedRiderMineCloseOtherAssetsNoncurrent_E1303AAA33C5FD1C480EF92C29EBD5F0" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CommitmentsGuaranteesAndContingenciesTextualsAbstract_D306F600406F87096F3CF92C29EBD497" xlink:to="loc_aep_AmountCollectedRiderMineCloseOtherAssetsNoncurrent_E1303AAA33C5FD1C480EF92C29EBD5F0" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaximumPotentialAmountofFuturePaymentsAssociatedwithGuarantee" xlink:label="loc_aep_MaximumPotentialAmountofFuturePaymentsAssociatedwithGuarantee_B1392C40F8ACA789BC65F92C29EB61A6" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CommitmentsGuaranteesAndContingenciesTextualsAbstract_D306F600406F87096F3CF92C29EBD497" xlink:to="loc_aep_MaximumPotentialAmountofFuturePaymentsAssociatedwithGuarantee_B1392C40F8ACA789BC65F92C29EB61A6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDue" xlink:label="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsDue_F0F1F2952C682FEFF4B3F92C29EC25CA" xlink:type="locator" />
    <link:definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CommitmentsGuaranteesAndContingenciesTextualsAbstract_D306F600406F87096F3CF92C29EBD497" xlink:to="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsDue_F0F1F2952C682FEFF4B3F92C29EC25CA" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SaleProceedsGuaranteedByLessorUnderCurrentFiveYearLeaseTerm" xlink:label="loc_aep_SaleProceedsGuaranteedByLessorUnderCurrentFiveYearLeaseTerm_C3E69623F6171DA7D7B0F92C29EC644D" xlink:type="locator" />
    <link:definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CommitmentsGuaranteesAndContingenciesTextualsAbstract_D306F600406F87096F3CF92C29EBD497" xlink:to="loc_aep_SaleProceedsGuaranteedByLessorUnderCurrentFiveYearLeaseTerm_C3E69623F6171DA7D7B0F92C29EC644D" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SaleProceedsGuaranteedByLessorAtEndOfTwentyYearTerm" xlink:label="loc_aep_SaleProceedsGuaranteedByLessorAtEndOfTwentyYearTerm_A7DE0490C4D76CA6CB66F92C29ECDB3F" xlink:type="locator" />
    <link:definitionArc order="15" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CommitmentsGuaranteesAndContingenciesTextualsAbstract_D306F600406F87096F3CF92C29EBD497" xlink:to="loc_aep_SaleProceedsGuaranteedByLessorAtEndOfTwentyYearTerm_A7DE0490C4D76CA6CB66F92C29ECDB3F" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaximumPotentialLossRelatedToGuarantee" xlink:label="loc_aep_MaximumPotentialLossRelatedToGuarantee_33C0C8FEEB2D52E5263EF92C29EC3DD2" xlink:type="locator" />
    <link:definitionArc order="16" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CommitmentsGuaranteesAndContingenciesTextualsAbstract_D306F600406F87096F3CF92C29EBD497" xlink:to="loc_aep_MaximumPotentialLossRelatedToGuarantee_33C0C8FEEB2D52E5263EF92C29EC3DD2" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaximumPotentialLeasePaymentsAEPROBargeandBoatLeases" xlink:label="loc_aep_MaximumPotentialLeasePaymentsAEPROBargeandBoatLeases_14C2E3149FEAAB2AD1F1F92C29EC9E9D" xlink:type="locator" />
    <link:definitionArc order="17" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CommitmentsGuaranteesAndContingenciesTextualsAbstract_D306F600406F87096F3CF92C29EBD497" xlink:to="loc_aep_MaximumPotentialLeasePaymentsAEPROBargeandBoatLeases_14C2E3149FEAAB2AD1F1F92C29EC9E9D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GuaranteeObligationsCurrentCarryingValue" xlink:label="loc_us-gaap_GuaranteeObligationsCurrentCarryingValue_A9E3B4607C0BA3AB3453F92C29EC77CC" xlink:type="locator" />
    <link:definitionArc order="18" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CommitmentsGuaranteesAndContingenciesTextualsAbstract_D306F600406F87096F3CF92C29EBD497" xlink:to="loc_us-gaap_GuaranteeObligationsCurrentCarryingValue_A9E3B4607C0BA3AB3453F92C29EC77CC" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_GuaranteeObligationsCurrentCarryingValueOtherLiabilitiesCurrent" xlink:label="loc_aep_GuaranteeObligationsCurrentCarryingValueOtherLiabilitiesCurrent_9BF942408202D50049A8F92C29EC4742" xlink:type="locator" />
    <link:definitionArc order="19" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CommitmentsGuaranteesAndContingenciesTextualsAbstract_D306F600406F87096F3CF92C29EBD497" xlink:to="loc_aep_GuaranteeObligationsCurrentCarryingValueOtherLiabilitiesCurrent_9BF942408202D50049A8F92C29EC4742" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_GuaranteeObligationsCurrentCarryingValueOtherLiabilitiesNoncurrent" xlink:label="loc_aep_GuaranteeObligationsCurrentCarryingValueOtherLiabilitiesNoncurrent_56EB2781A3E496801F1DF92C29EC5A4F" xlink:type="locator" />
    <link:definitionArc order="20" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CommitmentsGuaranteesAndContingenciesTextualsAbstract_D306F600406F87096F3CF92C29EBD497" xlink:to="loc_aep_GuaranteeObligationsCurrentCarryingValueOtherLiabilitiesNoncurrent_56EB2781A3E496801F1DF92C29EC5A4F" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/CommitmentsGuaranteesAndContingenciesTables" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_9C80AD303AD70511B6849C41A728847D" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_26DB56A5D34510EB1C2F9C41A72762A3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_9C80AD303AD70511B6849C41A728847D" xlink:to="loc_us-gaap_StatementTable_26DB56A5D34510EB1C2F9C41A72762A3" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_5615D9BF44BEDD16F0969C41A7270954" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_26DB56A5D34510EB1C2F9C41A72762A3" xlink:to="loc_dei_LegalEntityAxis_5615D9BF44BEDD16F0969C41A7270954" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_B4F74CF7A567DFE67F4D9C41A727C21F_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_5615D9BF44BEDD16F0969C41A7270954" xlink:to="loc_dei_EntityDomain_B4F74CF7A567DFE67F4D9C41A727C21F_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_B4F74CF7A567DFE67F4D9C41A727C21F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_5615D9BF44BEDD16F0969C41A7270954" xlink:to="loc_dei_EntityDomain_B4F74CF7A567DFE67F4D9C41A727C21F" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaximumFuturePaymentsforLettersofCreditUncommittedFacilitiesTableTextBlock" xlink:label="loc_aep_MaximumFuturePaymentsforLettersofCreditUncommittedFacilitiesTableTextBlock_DD70E4120678CBE39E939C41A7281F9A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9C80AD303AD70511B6849C41A728847D" xlink:to="loc_aep_MaximumFuturePaymentsforLettersofCreditUncommittedFacilitiesTableTextBlock_DD70E4120678CBE39E939C41A7281F9A" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaximumPotentialLossOnMasterLeaseAgreementsTextBlock" xlink:label="loc_aep_MaximumPotentialLossOnMasterLeaseAgreementsTextBlock_56E837A7656C93F09C459C41A728B0A6" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9C80AD303AD70511B6849C41A728847D" xlink:to="loc_aep_MaximumPotentialLossOnMasterLeaseAgreementsTextBlock_56E837A7656C93F09C459C41A728B0A6" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/ComprehensiveIncome" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_C8D4D18D71E87302B14FFD0AECB4E7FD" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_652B9DD4D1581A02C3BFFD0AECB38165" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_C8D4D18D71E87302B14FFD0AECB4E7FD" xlink:to="loc_us-gaap_StatementTable_652B9DD4D1581A02C3BFFD0AECB38165" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_767172D415925192C422FD0AECB376EA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_652B9DD4D1581A02C3BFFD0AECB38165" xlink:to="loc_dei_LegalEntityAxis_767172D415925192C422FD0AECB376EA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_F15C737A4F7C8072ACAFFD0AECB4042F_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_767172D415925192C422FD0AECB376EA" xlink:to="loc_dei_EntityDomain_F15C737A4F7C8072ACAFFD0AECB4042F_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_F15C737A4F7C8072ACAFFD0AECB4042F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_767172D415925192C422FD0AECB376EA" xlink:to="loc_dei_EntityDomain_F15C737A4F7C8072ACAFFD0AECB4042F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ComprehensiveIncomeNoteTextBlock" xlink:label="loc_us-gaap_ComprehensiveIncomeNoteTextBlock_EF0BEB3CDEF3BED7A90BFD0AECB482FB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_C8D4D18D71E87302B14FFD0AECB4E7FD" xlink:to="loc_us-gaap_ComprehensiveIncomeNoteTextBlock_EF0BEB3CDEF3BED7A90BFD0AECB482FB" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/ComprehensiveIncomeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_815464F56689511677BBF7C3BBE8E6ED" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_0570A3B55EBFA36DED7FF7C3BBE45B8E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_815464F56689511677BBF7C3BBE8E6ED" xlink:to="loc_us-gaap_StatementTable_0570A3B55EBFA36DED7FF7C3BBE45B8E" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_94120B758D5DF1E1CD31F7C3BBE62C88" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_0570A3B55EBFA36DED7FF7C3BBE45B8E" xlink:to="loc_dei_LegalEntityAxis_94120B758D5DF1E1CD31F7C3BBE62C88" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_3884D85524668F8CD3B9F7C3BBE677CD_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_94120B758D5DF1E1CD31F7C3BBE62C88" xlink:to="loc_dei_EntityDomain_3884D85524668F8CD3B9F7C3BBE677CD_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_3884D85524668F8CD3B9F7C3BBE677CD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_94120B758D5DF1E1CD31F7C3BBE62C88" xlink:to="loc_dei_EntityDomain_3884D85524668F8CD3B9F7C3BBE677CD" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTexasInc.Member" xlink:label="loc_aep_AEPTexasInc.Member_E16F38DF2B6202E06998F7C3BBE6A9AE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_3884D85524668F8CD3B9F7C3BBE677CD" xlink:to="loc_aep_AEPTexasInc.Member_E16F38DF2B6202E06998F7C3BBE6A9AE" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTransmissionCoMember" xlink:label="loc_aep_AEPTransmissionCoMember_14348EC9772F6E7C16E0F7C3BBE6056D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_3884D85524668F8CD3B9F7C3BBE677CD" xlink:to="loc_aep_AEPTransmissionCoMember_14348EC9772F6E7C16E0F7C3BBE6056D" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AppalachianPowerCoMember" xlink:label="loc_aep_AppalachianPowerCoMember_851D2EB68A775D71F602F7E5F814FF4B" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_3884D85524668F8CD3B9F7C3BBE677CD" xlink:to="loc_aep_AppalachianPowerCoMember_851D2EB68A775D71F602F7E5F814FF4B" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IndianaMichiganPowerCoMember" xlink:label="loc_aep_IndianaMichiganPowerCoMember_B2EA454DC99FCAE9905EF7C3BBE60B28" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_3884D85524668F8CD3B9F7C3BBE677CD" xlink:to="loc_aep_IndianaMichiganPowerCoMember_B2EA454DC99FCAE9905EF7C3BBE60B28" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OhioPowerCoMember" xlink:label="loc_aep_OhioPowerCoMember_5DA9ADB51EBF6F503618F7C3BBE688A7" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_3884D85524668F8CD3B9F7C3BBE677CD" xlink:to="loc_aep_OhioPowerCoMember_5DA9ADB51EBF6F503618F7C3BBE688A7" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_PublicServiceCoOfOklahomaMember" xlink:label="loc_aep_PublicServiceCoOfOklahomaMember_01ABC12531F484F81AAEF7C3BBE63284" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_3884D85524668F8CD3B9F7C3BBE677CD" xlink:to="loc_aep_PublicServiceCoOfOklahomaMember_01ABC12531F484F81AAEF7C3BBE63284" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SouthwesternElectricPowerCoMember" xlink:label="loc_aep_SouthwesternElectricPowerCoMember_3C4D64E9FDAE6142C53AF7C3BBE7EE4B" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_3884D85524668F8CD3B9F7C3BBE677CD" xlink:to="loc_aep_SouthwesternElectricPowerCoMember_3C4D64E9FDAE6142C53AF7C3BBE7EE4B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_0218078965C33987047FF7C3BBE721B7" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_0570A3B55EBFA36DED7FF7C3BBE45B8E" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_0218078965C33987047FF7C3BBE721B7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_6D75F6D5E7683B0471E2F7C3BBE7291B_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_0218078965C33987047FF7C3BBE721B7" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_6D75F6D5E7683B0471E2F7C3BBE7291B_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_6D75F6D5E7683B0471E2F7C3BBE7291B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_0218078965C33987047FF7C3BBE721B7" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_6D75F6D5E7683B0471E2F7C3BBE7291B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_81532537BB50D86484CFF7C3BBE792FC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_6D75F6D5E7683B0471E2F7C3BBE7291B" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_81532537BB50D86484CFF7C3BBE792FC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_5FC946E1D45AB5DE6A3FF7C3BBE787C3" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_0570A3B55EBFA36DED7FF7C3BBE45B8E" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_5FC946E1D45AB5DE6A3FF7C3BBE787C3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_CF45F83E529C2E2913C7F7C3BBE7A178_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_5FC946E1D45AB5DE6A3FF7C3BBE787C3" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_CF45F83E529C2E2913C7F7C3BBE7A178_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_CF45F83E529C2E2913C7F7C3BBE7A178" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_5FC946E1D45AB5DE6A3FF7C3BBE787C3" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_CF45F83E529C2E2913C7F7C3BBE7A178" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommodityContractMember" xlink:label="loc_us-gaap_CommodityContractMember_43BDB827D9FD1C13570EF7C3BBE7A0DE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_CF45F83E529C2E2913C7F7C3BBE7A178" xlink:to="loc_us-gaap_CommodityContractMember_43BDB827D9FD1C13570EF7C3BBE7A0DE" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_InterestRateMember" xlink:label="loc_aep_InterestRateMember_1BC8586D007660D7FE2EF7C3BBE724AD" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_CF45F83E529C2E2913C7F7C3BBE7A178" xlink:to="loc_aep_InterestRateMember_1BC8586D007660D7FE2EF7C3BBE724AD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_7A277EE533355681083FF7C3BBE74CA5" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_0570A3B55EBFA36DED7FF7C3BBE45B8E" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_7A277EE533355681083FF7C3BBE74CA5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_E133DDA9BC7B7E375E38F7C3BBE743A5_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_7A277EE533355681083FF7C3BBE74CA5" xlink:to="loc_us-gaap_EquityComponentDomain_E133DDA9BC7B7E375E38F7C3BBE743A5_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_E133DDA9BC7B7E375E38F7C3BBE743A5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_7A277EE533355681083FF7C3BBE74CA5" xlink:to="loc_us-gaap_EquityComponentDomain_E133DDA9BC7B7E375E38F7C3BBE743A5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember" xlink:label="loc_us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember_0DCB0B3B1DB993F78645F7C3BBE8F018" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_E133DDA9BC7B7E375E38F7C3BBE743A5" xlink:to="loc_us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember_0DCB0B3B1DB993F78645F7C3BBE8F018" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember" xlink:label="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_96924FC07F6FE2C6A582F7C3BBE81147" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_E133DDA9BC7B7E375E38F7C3BBE743A5" xlink:to="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_96924FC07F6FE2C6A582F7C3BBE81147" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_476BBA2AAF1C95B0FB03F7C3BBE80D68" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_E133DDA9BC7B7E375E38F7C3BBE743A5" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_476BBA2AAF1C95B0FB03F7C3BBE80D68" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_732D2D86740A9FDE2639F7C3BBE80B5A" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_E133DDA9BC7B7E375E38F7C3BBE743A5" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_732D2D86740A9FDE2639F7C3BBE80B5A" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ChangesInAccumulatedOtherComprehensiveIncomeByComponentAbstract" xlink:label="loc_aep_ChangesInAccumulatedOtherComprehensiveIncomeByComponentAbstract_EFB2678D4A303950B319F7C3BBE86876" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_815464F56689511677BBF7C3BBE8E6ED" xlink:to="loc_aep_ChangesInAccumulatedOtherComprehensiveIncomeByComponentAbstract_EFB2678D4A303950B319F7C3BBE86876" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_64AB86A7C75B01077998F7C3BBE8D032" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_ChangesInAccumulatedOtherComprehensiveIncomeByComponentAbstract_EFB2678D4A303950B319F7C3BBE86876" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_64AB86A7C75B01077998F7C3BBE8D032" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OtherComprehensiveIncomeUnrealizedGainLossArisingDuringPeriodNetOfTax" xlink:label="loc_aep_OtherComprehensiveIncomeUnrealizedGainLossArisingDuringPeriodNetOfTax_0D869FBF5FFD37B19F9AF7C3BBE87F7F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_ChangesInAccumulatedOtherComprehensiveIncomeByComponentAbstract_EFB2678D4A303950B319F7C3BBE86876" xlink:to="loc_aep_OtherComprehensiveIncomeUnrealizedGainLossArisingDuringPeriodNetOfTax_0D869FBF5FFD37B19F9AF7C3BBE87F7F" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ReclassificationsFromAccumulatedOtherComprehensiveIncomeAbstract" xlink:label="loc_aep_ReclassificationsFromAccumulatedOtherComprehensiveIncomeAbstract_4EE5B2030337DB9736FFF7C3BBE87CFE" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_ChangesInAccumulatedOtherComprehensiveIncomeByComponentAbstract_EFB2678D4A303950B319F7C3BBE86876" xlink:to="loc_aep_ReclassificationsFromAccumulatedOtherComprehensiveIncomeAbstract_4EE5B2030337DB9736FFF7C3BBE87CFE" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_CommodityAbstract" xlink:label="loc_aep_CommodityAbstract_53B924B32DF57A36A2BAF7C3BBE81F08" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_ReclassificationsFromAccumulatedOtherComprehensiveIncomeAbstract_4EE5B2030337DB9736FFF7C3BBE87CFE" xlink:to="loc_aep_CommodityAbstract_53B924B32DF57A36A2BAF7C3BBE81F08" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ElectricalGenerationRevenue" xlink:label="loc_us-gaap_ElectricalGenerationRevenue_A532F69E368D123286ADF8779C1E3959" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CommodityAbstract_53B924B32DF57A36A2BAF7C3BBE81F08" xlink:to="loc_us-gaap_ElectricalGenerationRevenue_A532F69E368D123286ADF8779C1E3959" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CostOfPurchasedPower" xlink:label="loc_us-gaap_CostOfPurchasedPower_7458DC0B7D053EF7D463F7C3BBE845C8" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CommodityAbstract_53B924B32DF57A36A2BAF7C3BBE81F08" xlink:to="loc_us-gaap_CostOfPurchasedPower_7458DC0B7D053EF7D463F7C3BBE845C8" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_InterestRateAbstract" xlink:label="loc_aep_InterestRateAbstract_CCA9A7B1FB56B02755DAF7C3BBE8CDA9" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_ReclassificationsFromAccumulatedOtherComprehensiveIncomeAbstract_4EE5B2030337DB9736FFF7C3BBE87CFE" xlink:to="loc_aep_InterestRateAbstract_CCA9A7B1FB56B02755DAF7C3BBE8CDA9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InterestExpense" xlink:label="loc_us-gaap_InterestExpense_743BBD689D0B93CE00E2F7C3BBE8F47D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_InterestRateAbstract_CCA9A7B1FB56B02755DAF7C3BBE8CDA9" xlink:to="loc_us-gaap_InterestExpense_743BBD689D0B93CE00E2F7C3BBE8F47D" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AmortizationOfPensionAndOtherPostretirementBenefitPlansAbstract" xlink:label="loc_aep_AmortizationOfPensionAndOtherPostretirementBenefitPlansAbstract_1A8FF383555A9D75AB77F7C3BBE97948" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_ReclassificationsFromAccumulatedOtherComprehensiveIncomeAbstract_4EE5B2030337DB9736FFF7C3BBE87CFE" xlink:to="loc_aep_AmortizationOfPensionAndOtherPostretirementBenefitPlansAbstract_1A8FF383555A9D75AB77F7C3BBE97948" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditBeforeTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditBeforeTax_2D856F3B08CE2444B4F0F7C3BBE9BAD5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_AmortizationOfPensionAndOtherPostretirementBenefitPlansAbstract_1A8FF383555A9D75AB77F7C3BBE97948" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditBeforeTax_2D856F3B08CE2444B4F0F7C3BBE9BAD5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax_1D17588DAE1DF742C806F7C3BBE9F954" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_AmortizationOfPensionAndOtherPostretirementBenefitPlansAbstract_1A8FF383555A9D75AB77F7C3BBE97948" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax_1D17588DAE1DF742C806F7C3BBE9F954" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_F2CF58884A5D5D841495F7C3BBE9B99A" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_ChangesInAccumulatedOtherComprehensiveIncomeByComponentAbstract_EFB2678D4A303950B319F7C3BBE86876" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_F2CF58884A5D5D841495F7C3BBE9B99A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_2DB344F447AA97E60711F7C3BBE93194" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_ChangesInAccumulatedOtherComprehensiveIncomeByComponentAbstract_EFB2678D4A303950B319F7C3BBE86876" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_2DB344F447AA97E60711F7C3BBE93194" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_CAEFC0AFF6E5992AF2A5F7C3BBE9F8DC" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_ChangesInAccumulatedOtherComprehensiveIncomeByComponentAbstract_EFB2678D4A303950B319F7C3BBE86876" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_CAEFC0AFF6E5992AF2A5F7C3BBE9F8DC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_1B3D9C5F95D3CD49FEABF7C3BBE94BF3" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_ChangesInAccumulatedOtherComprehensiveIncomeByComponentAbstract_EFB2678D4A303950B319F7C3BBE86876" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_1B3D9C5F95D3CD49FEABF7C3BBE94BF3" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_StockholdersEquityASU201802Adoption" xlink:label="loc_aep_StockholdersEquityASU201802Adoption_2A1CAF94E20655C5C76CF7C3BBE9EF0F" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_ChangesInAccumulatedOtherComprehensiveIncomeByComponentAbstract_EFB2678D4A303950B319F7C3BBE86876" xlink:to="loc_aep_StockholdersEquityASU201802Adoption_2A1CAF94E20655C5C76CF7C3BBE9EF0F" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_StockholdersEquityASU201601Adoption" xlink:label="loc_aep_StockholdersEquityASU201601Adoption_ECE36B03C49316B0A6ECF7C3BBE939D1" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_ChangesInAccumulatedOtherComprehensiveIncomeByComponentAbstract_EFB2678D4A303950B319F7C3BBE86876" xlink:to="loc_aep_StockholdersEquityASU201601Adoption_ECE36B03C49316B0A6ECF7C3BBE939D1" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/ComprehensiveIncomeTables" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_81CBC512D35F0B4F71F7FD0AECB0DB23" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_112646F048A506BE0D1CFD0AECAF2EFE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_81CBC512D35F0B4F71F7FD0AECB0DB23" xlink:to="loc_us-gaap_StatementTable_112646F048A506BE0D1CFD0AECAF2EFE" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_B7012C7491847E7885B8FD0AECAFC8D0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_112646F048A506BE0D1CFD0AECAF2EFE" xlink:to="loc_dei_LegalEntityAxis_B7012C7491847E7885B8FD0AECAFC8D0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_F71A4F49077C5E84860BFD0AECAF2CBB_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_B7012C7491847E7885B8FD0AECAFC8D0" xlink:to="loc_dei_EntityDomain_F71A4F49077C5E84860BFD0AECAF2CBB_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_F71A4F49077C5E84860BFD0AECAF2CBB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_B7012C7491847E7885B8FD0AECAFC8D0" xlink:to="loc_dei_EntityDomain_F71A4F49077C5E84860BFD0AECAF2CBB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfAccumulatedOtherComprehensiveIncomeLossTableTextBlock" xlink:label="loc_us-gaap_ScheduleOfAccumulatedOtherComprehensiveIncomeLossTableTextBlock_E00EC2228BEEC0CD4BD9FD0AECB0E2B6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_81CBC512D35F0B4F71F7FD0AECB0DB23" xlink:to="loc_us-gaap_ScheduleOfAccumulatedOtherComprehensiveIncomeLossTableTextBlock_E00EC2228BEEC0CD4BD9FD0AECB0E2B6" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/CondensedConsolidatedBalanceSheets" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_9D4947F5977D7A467B1AF3B0FD7D02D1" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_F3E7BDAE0FF4E25191EEF3B0FD7DFE54" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_9D4947F5977D7A467B1AF3B0FD7D02D1" xlink:to="loc_us-gaap_StatementTable_F3E7BDAE0FF4E25191EEF3B0FD7DFE54" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_3F66647A426E5800F42CF3B0FD7D6FD3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_F3E7BDAE0FF4E25191EEF3B0FD7DFE54" xlink:to="loc_dei_LegalEntityAxis_3F66647A426E5800F42CF3B0FD7D6FD3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_C932328023115E2C9EDEF3B0FD7D0040_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_3F66647A426E5800F42CF3B0FD7D6FD3" xlink:to="loc_dei_EntityDomain_C932328023115E2C9EDEF3B0FD7D0040_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_C932328023115E2C9EDEF3B0FD7D0040" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_3F66647A426E5800F42CF3B0FD7D6FD3" xlink:to="loc_dei_EntityDomain_C932328023115E2C9EDEF3B0FD7D0040" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTexasInc.Member" xlink:label="loc_aep_AEPTexasInc.Member_345CD0E88E9E67F1B7A2F3B0FD7DDE45" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_C932328023115E2C9EDEF3B0FD7D0040" xlink:to="loc_aep_AEPTexasInc.Member_345CD0E88E9E67F1B7A2F3B0FD7DDE45" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTransmissionCoMember" xlink:label="loc_aep_AEPTransmissionCoMember_41A033C628FB31248BBFF3B0FD7D0286" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_C932328023115E2C9EDEF3B0FD7D0040" xlink:to="loc_aep_AEPTransmissionCoMember_41A033C628FB31248BBFF3B0FD7D0286" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AppalachianPowerCoMember" xlink:label="loc_aep_AppalachianPowerCoMember_DD72DF49A5D76A3B0F06F3B0FD7DA253" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_C932328023115E2C9EDEF3B0FD7D0040" xlink:to="loc_aep_AppalachianPowerCoMember_DD72DF49A5D76A3B0F06F3B0FD7DA253" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IndianaMichiganPowerCoMember" xlink:label="loc_aep_IndianaMichiganPowerCoMember_522076788A99461B5765F3B0FD7DB0C3" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_C932328023115E2C9EDEF3B0FD7D0040" xlink:to="loc_aep_IndianaMichiganPowerCoMember_522076788A99461B5765F3B0FD7DB0C3" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OhioPowerCoMember" xlink:label="loc_aep_OhioPowerCoMember_26D495DF6AE7386B6754F3B0FD7D1D72" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_C932328023115E2C9EDEF3B0FD7D0040" xlink:to="loc_aep_OhioPowerCoMember_26D495DF6AE7386B6754F3B0FD7D1D72" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_PublicServiceCoOfOklahomaMember" xlink:label="loc_aep_PublicServiceCoOfOklahomaMember_8D078E12F39834FC3A88F3B0FD7D78A3" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_C932328023115E2C9EDEF3B0FD7D0040" xlink:to="loc_aep_PublicServiceCoOfOklahomaMember_8D078E12F39834FC3A88F3B0FD7D78A3" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SouthwesternElectricPowerCoMember" xlink:label="loc_aep_SouthwesternElectricPowerCoMember_D6027C59AF83538B0558F3B0FD7DC616" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_C932328023115E2C9EDEF3B0FD7D0040" xlink:to="loc_aep_SouthwesternElectricPowerCoMember_D6027C59AF83538B0558F3B0FD7DC616" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetsCurrentAbstract" xlink:label="loc_us-gaap_AssetsCurrentAbstract_22D92AA82D28888ABE8FF3B0FD7D94C9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9D4947F5977D7A467B1AF3B0FD7D02D1" xlink:to="loc_us-gaap_AssetsCurrentAbstract_22D92AA82D28888ABE8FF3B0FD7D94C9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_6E6A8BED9422D9DC4FA6F3B0FD7DB183" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_22D92AA82D28888ABE8FF3B0FD7D94C9" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_6E6A8BED9422D9DC4FA6F3B0FD7DB183" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue_ADE935FD8114B3AD6996F3B0FD7D2C55" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_22D92AA82D28888ABE8FF3B0FD7D94C9" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue_ADE935FD8114B3AD6996F3B0FD7D2C55" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShortTermInvestments" xlink:label="loc_us-gaap_ShortTermInvestments_92BD0C7C31EC3AE1E42EF3B0FD7D6BF6" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_22D92AA82D28888ABE8FF3B0FD7D94C9" xlink:to="loc_us-gaap_ShortTermInvestments_92BD0C7C31EC3AE1E42EF3B0FD7D6BF6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DueFromRelatedPartiesCurrent" xlink:label="loc_us-gaap_DueFromRelatedPartiesCurrent_8E4CF377D3BE5402ED88F3B0FD7DA45D" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_22D92AA82D28888ABE8FF3B0FD7D94C9" xlink:to="loc_us-gaap_DueFromRelatedPartiesCurrent_8E4CF377D3BE5402ED88F3B0FD7DA45D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountsReceivableNetCurrentAbstract" xlink:label="loc_us-gaap_AccountsReceivableNetCurrentAbstract_264A6803AE47C689BA74F3B0FD7DD49B" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_22D92AA82D28888ABE8FF3B0FD7D94C9" xlink:to="loc_us-gaap_AccountsReceivableNetCurrentAbstract_264A6803AE47C689BA74F3B0FD7DD49B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountsReceivableGrossCurrent" xlink:label="loc_us-gaap_AccountsReceivableGrossCurrent_D85847A66E0DA0FE0EB2F3B0FD7D207D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsReceivableNetCurrentAbstract_264A6803AE47C689BA74F3B0FD7DD49B" xlink:to="loc_us-gaap_AccountsReceivableGrossCurrent_D85847A66E0DA0FE0EB2F3B0FD7D207D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountsReceivableRelatedPartiesCurrent" xlink:label="loc_us-gaap_AccountsReceivableRelatedPartiesCurrent_0A2C8643E298B20814B0F3B0FD7D857F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsReceivableNetCurrentAbstract_264A6803AE47C689BA74F3B0FD7DD49B" xlink:to="loc_us-gaap_AccountsReceivableRelatedPartiesCurrent_0A2C8643E298B20814B0F3B0FD7D857F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_UnbilledReceivablesCurrent" xlink:label="loc_us-gaap_UnbilledReceivablesCurrent_DA3B1D4CD90898CCC620F3B0FD7D3006" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsReceivableNetCurrentAbstract_264A6803AE47C689BA74F3B0FD7DD49B" xlink:to="loc_us-gaap_UnbilledReceivablesCurrent_DA3B1D4CD90898CCC620F3B0FD7D3006" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TransfersAccountedForAsSecuredBorrowingsAssetsCarryingAmount" xlink:label="loc_us-gaap_TransfersAccountedForAsSecuredBorrowingsAssetsCarryingAmount_7C7790461DA13262E242F3B0FD7D1AF7" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsReceivableNetCurrentAbstract_264A6803AE47C689BA74F3B0FD7DD49B" xlink:to="loc_us-gaap_TransfersAccountedForAsSecuredBorrowingsAssetsCarryingAmount_7C7790461DA13262E242F3B0FD7D1AF7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherReceivables" xlink:label="loc_us-gaap_OtherReceivables_D65A24EF5EC148601862F3B0FD7DFBF5" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsReceivableNetCurrentAbstract_264A6803AE47C689BA74F3B0FD7DD49B" xlink:to="loc_us-gaap_OtherReceivables_D65A24EF5EC148601862F3B0FD7DFBF5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_616CCBFDF364CE937805F3B0FD7DE25D" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsReceivableNetCurrentAbstract_264A6803AE47C689BA74F3B0FD7DD49B" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_616CCBFDF364CE937805F3B0FD7DE25D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountsReceivableNetCurrent" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_46DAD7C099189390E83FF3B0FD7DCA8A" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsReceivableNetCurrentAbstract_264A6803AE47C689BA74F3B0FD7DD49B" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_46DAD7C099189390E83FF3B0FD7DCA8A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InventoryRawMaterials" xlink:label="loc_us-gaap_InventoryRawMaterials_B392AA21B0399DEB6B90F3B0FD7DDD6A" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_22D92AA82D28888ABE8FF3B0FD7D94C9" xlink:to="loc_us-gaap_InventoryRawMaterials_B392AA21B0399DEB6B90F3B0FD7DDD6A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherInventorySupplies" xlink:label="loc_us-gaap_OtherInventorySupplies_E5D174F0C0C8D65CC323F3B0FD7DA61C" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_22D92AA82D28888ABE8FF3B0FD7D94C9" xlink:to="loc_us-gaap_OtherInventorySupplies_E5D174F0C0C8D65CC323F3B0FD7DA61C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RenewableEnergyCredits" xlink:label="loc_aep_RenewableEnergyCredits_9C62F9D643E8D2C1F21FF3B0FD7D34DC" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_22D92AA82D28888ABE8FF3B0FD7D94C9" xlink:to="loc_aep_RenewableEnergyCredits_9C62F9D643E8D2C1F21FF3B0FD7D34DC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeAssetsCurrent" xlink:label="loc_us-gaap_DerivativeAssetsCurrent_CE352A61B5BE4E3BAD84F3B0FD7DB518" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_22D92AA82D28888ABE8FF3B0FD7D94C9" xlink:to="loc_us-gaap_DerivativeAssetsCurrent_CE352A61B5BE4E3BAD84F3B0FD7DB518" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeTaxesReceivable" xlink:label="loc_us-gaap_IncomeTaxesReceivable_11CEFBAAE394A1A055EFF3B0FD7DE2C8" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_22D92AA82D28888ABE8FF3B0FD7D94C9" xlink:to="loc_us-gaap_IncomeTaxesReceivable_11CEFBAAE394A1A055EFF3B0FD7DE2C8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RegulatoryAssetsCurrent" xlink:label="loc_us-gaap_RegulatoryAssetsCurrent_4A9E504C38A20223DBC0F3B0FD7D79AC" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_22D92AA82D28888ABE8FF3B0FD7D94C9" xlink:to="loc_us-gaap_RegulatoryAssetsCurrent_4A9E504C38A20223DBC0F3B0FD7D79AC" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AccruedReimbursementofSpentNuclearFuelCosts" xlink:label="loc_aep_AccruedReimbursementofSpentNuclearFuelCosts_EFCBED890EE040C2E1CDF3B0FD7DC422" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_22D92AA82D28888ABE8FF3B0FD7D94C9" xlink:to="loc_aep_AccruedReimbursementofSpentNuclearFuelCosts_EFCBED890EE040C2E1CDF3B0FD7DC422" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MarginDepositAssets" xlink:label="loc_us-gaap_MarginDepositAssets_B91A54BFA6BFF78E9E65F3B0FD7DA9C3" xlink:type="locator" />
    <link:definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_22D92AA82D28888ABE8FF3B0FD7D94C9" xlink:to="loc_us-gaap_MarginDepositAssets_B91A54BFA6BFF78E9E65F3B0FD7DA9C3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_3DB839C4AF9E44ADAA2FF3B0FD7D28B5" xlink:type="locator" />
    <link:definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_22D92AA82D28888ABE8FF3B0FD7D94C9" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_3DB839C4AF9E44ADAA2FF3B0FD7D28B5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetsCurrent" xlink:label="loc_us-gaap_AssetsCurrent_73FE878B2ADA7E49D5BBF3B0FD7D8BF6" xlink:type="locator" />
    <link:definitionArc order="15" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_22D92AA82D28888ABE8FF3B0FD7D94C9" xlink:to="loc_us-gaap_AssetsCurrent_73FE878B2ADA7E49D5BBF3B0FD7D8BF6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentGrossAbstract" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGrossAbstract_06FEEC3622AAC1674BE6F3B0FD7D9DDF" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9D4947F5977D7A467B1AF3B0FD7D02D1" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGrossAbstract_06FEEC3622AAC1674BE6F3B0FD7D9DDF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PublicUtilitiesPropertyPlantAndEquipmentGenerationOrProcessing" xlink:label="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentGenerationOrProcessing_75EC8C29EF9DF3BB44F0F3B0FD7D7D10" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentGrossAbstract_06FEEC3622AAC1674BE6F3B0FD7D9DDF" xlink:to="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentGenerationOrProcessing_75EC8C29EF9DF3BB44F0F3B0FD7D7D10" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PublicUtilitiesPropertyPlantAndEquipmentTransmission" xlink:label="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentTransmission_3DC7792A829901752071F3B0FD7DE991" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentGrossAbstract_06FEEC3622AAC1674BE6F3B0FD7D9DDF" xlink:to="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentTransmission_3DC7792A829901752071F3B0FD7DE991" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDistribution" xlink:label="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDistribution_262826A76E4F952281ACF3B0FD7D2216" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentGrossAbstract_06FEEC3622AAC1674BE6F3B0FD7D9DDF" xlink:to="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDistribution_262826A76E4F952281ACF3B0FD7D2216" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PublicUtilitiesPropertyPlantAndEquipmentOtherPropertyPlantAndEquipment" xlink:label="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentOtherPropertyPlantAndEquipment_3755CD7BA5D9B8D7DF41F3B0FD7DC78D" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentGrossAbstract_06FEEC3622AAC1674BE6F3B0FD7D9DDF" xlink:to="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentOtherPropertyPlantAndEquipment_3755CD7BA5D9B8D7DF41F3B0FD7DC78D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConstructionInProgressGross" xlink:label="loc_us-gaap_ConstructionInProgressGross_69ED1146A168FA2C5D50F3B0FD7D1103" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentGrossAbstract_06FEEC3622AAC1674BE6F3B0FD7D9DDF" xlink:to="loc_us-gaap_ConstructionInProgressGross_69ED1146A168FA2C5D50F3B0FD7D1103" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentGross" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_0C6B56EEF1C8B9963F55F3B0FD7DC91A" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentGrossAbstract_06FEEC3622AAC1674BE6F3B0FD7D9DDF" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_0C6B56EEF1C8B9963F55F3B0FD7DC91A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_E7622354CEDF835BB512F3B0FD7D6DD4" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentGrossAbstract_06FEEC3622AAC1674BE6F3B0FD7D9DDF" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_E7622354CEDF835BB512F3B0FD7D6DD4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_2ABBEB3B43DEAAA18CA2F3B0FD7D8149" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentGrossAbstract_06FEEC3622AAC1674BE6F3B0FD7D9DDF" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_2ABBEB3B43DEAAA18CA2F3B0FD7D8149" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetsNoncurrentAbstract" xlink:label="loc_us-gaap_AssetsNoncurrentAbstract_18EE7B69CC64F282D34FF3B0FD7D3524" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9D4947F5977D7A467B1AF3B0FD7D02D1" xlink:to="loc_us-gaap_AssetsNoncurrentAbstract_18EE7B69CC64F282D34FF3B0FD7D3524" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RegulatoryAssetsNoncurrent" xlink:label="loc_us-gaap_RegulatoryAssetsNoncurrent_EBE12D5C6C80FC5502D1F3B0FD7D88D8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_18EE7B69CC64F282D34FF3B0FD7D3524" xlink:to="loc_us-gaap_RegulatoryAssetsNoncurrent_EBE12D5C6C80FC5502D1F3B0FD7D88D8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredTaxAssetsPropertyPlantAndEquipment" xlink:label="loc_us-gaap_DeferredTaxAssetsPropertyPlantAndEquipment_D358A438D27C0AE518CFF3B0FD7D2768" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_18EE7B69CC64F282D34FF3B0FD7D3524" xlink:to="loc_us-gaap_DeferredTaxAssetsPropertyPlantAndEquipment_D358A438D27C0AE518CFF3B0FD7D2768" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SecuritizedRegulatoryTransitionAssetsNoncurrent" xlink:label="loc_us-gaap_SecuritizedRegulatoryTransitionAssetsNoncurrent_DDAE4C66391B2A98E925F3B0FD7D21A0" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_18EE7B69CC64F282D34FF3B0FD7D3524" xlink:to="loc_us-gaap_SecuritizedRegulatoryTransitionAssetsNoncurrent_DDAE4C66391B2A98E925F3B0FD7D21A0" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SpentNuclearFuelAndDecommissioningTrusts" xlink:label="loc_aep_SpentNuclearFuelAndDecommissioningTrusts_4AA87B76850F8824CB5CF3B0FD7D3DFD" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_18EE7B69CC64F282D34FF3B0FD7D3524" xlink:to="loc_aep_SpentNuclearFuelAndDecommissioningTrusts_4AA87B76850F8824CB5CF3B0FD7D3DFD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Goodwill" xlink:label="loc_us-gaap_Goodwill_9F9A3D1F597816633FFBF3B0FD7DC8F9" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_18EE7B69CC64F282D34FF3B0FD7D3524" xlink:to="loc_us-gaap_Goodwill_9F9A3D1F597816633FFBF3B0FD7DC8F9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeAssetsNoncurrent" xlink:label="loc_us-gaap_DerivativeAssetsNoncurrent_69A1704C78D7A81E8D72F3B0FD7D5C1F" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_18EE7B69CC64F282D34FF3B0FD7D3524" xlink:to="loc_us-gaap_DerivativeAssetsNoncurrent_69A1704C78D7A81E8D72F3B0FD7D5C1F" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_EmployeeBenefitsAndPensionAssets" xlink:label="loc_aep_EmployeeBenefitsAndPensionAssets_B69D049F50094777AC1CF3B0FD7DA955" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_18EE7B69CC64F282D34FF3B0FD7D3524" xlink:to="loc_aep_EmployeeBenefitsAndPensionAssets_B69D049F50094777AC1CF3B0FD7DA955" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherAssetsNoncurrent" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_162D627EF892F0FEDF72F3B0FD7DFC21" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_18EE7B69CC64F282D34FF3B0FD7D3524" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_162D627EF892F0FEDF72F3B0FD7DFC21" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetsNoncurrent" xlink:label="loc_us-gaap_AssetsNoncurrent_851AFE45C9FE8AE2C9A5F3B0FD7D0E33" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_18EE7B69CC64F282D34FF3B0FD7D3524" xlink:to="loc_us-gaap_AssetsNoncurrent_851AFE45C9FE8AE2C9A5F3B0FD7D0E33" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Assets" xlink:label="loc_us-gaap_Assets_97D88871FB5620557C89F3B0FD7DF9CC" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9D4947F5977D7A467B1AF3B0FD7D02D1" xlink:to="loc_us-gaap_Assets_97D88871FB5620557C89F3B0FD7DF9CC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LiabilitiesCurrentAbstract" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_F230E74D359EFE7BA52DF3B0FD7DB707" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9D4947F5977D7A467B1AF3B0FD7D02D1" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_F230E74D359EFE7BA52DF3B0FD7DB707" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DueToRelatedPartiesCurrent" xlink:label="loc_us-gaap_DueToRelatedPartiesCurrent_E0FF5A35082F7E3DB94DF3B0FD7D72D3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_F230E74D359EFE7BA52DF3B0FD7DB707" xlink:to="loc_us-gaap_DueToRelatedPartiesCurrent_E0FF5A35082F7E3DB94DF3B0FD7D72D3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountsPayableCurrent" xlink:label="loc_us-gaap_AccountsPayableCurrent_AD64EC0F66A4DCCD6C38F3B0FD7D58FC" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_F230E74D359EFE7BA52DF3B0FD7DB707" xlink:to="loc_us-gaap_AccountsPayableCurrent_AD64EC0F66A4DCCD6C38F3B0FD7D58FC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountsPayableRelatedPartiesCurrent" xlink:label="loc_us-gaap_AccountsPayableRelatedPartiesCurrent_9782C2E45747B51A1C5BF3B0FD7D8F8B" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_F230E74D359EFE7BA52DF3B0FD7DB707" xlink:to="loc_us-gaap_AccountsPayableRelatedPartiesCurrent_9782C2E45747B51A1C5BF3B0FD7D8F8B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShortTermBorrowingsAbstract" xlink:label="loc_us-gaap_ShortTermBorrowingsAbstract_C72EC06D667DC2A6ACFBF3B0FD7DCC27" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_F230E74D359EFE7BA52DF3B0FD7DB707" xlink:to="loc_us-gaap_ShortTermBorrowingsAbstract_C72EC06D667DC2A6ACFBF3B0FD7DCC27" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TransfersAccountedForAsSecuredBorrowingsAssociatedLiabilitiesCarryingAmount" xlink:label="loc_us-gaap_TransfersAccountedForAsSecuredBorrowingsAssociatedLiabilitiesCarryingAmount_64D6E9B1BBD19611CD0EF3B0FD7DF6C1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermBorrowingsAbstract_C72EC06D667DC2A6ACFBF3B0FD7DCC27" xlink:to="loc_us-gaap_TransfersAccountedForAsSecuredBorrowingsAssociatedLiabilitiesCarryingAmount_64D6E9B1BBD19611CD0EF3B0FD7DF6C1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShortTermBankLoansAndNotesPayable" xlink:label="loc_us-gaap_ShortTermBankLoansAndNotesPayable_2CEF9870A5D15EF0F2F2F3B0FD7D4119" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermBorrowingsAbstract_C72EC06D667DC2A6ACFBF3B0FD7DCC27" xlink:to="loc_us-gaap_ShortTermBankLoansAndNotesPayable_2CEF9870A5D15EF0F2F2F3B0FD7D4119" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShortTermBorrowings" xlink:label="loc_us-gaap_ShortTermBorrowings_8D977989BB735B983270F3B0FD7D8EC1" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermBorrowingsAbstract_C72EC06D667DC2A6ACFBF3B0FD7DCC27" xlink:to="loc_us-gaap_ShortTermBorrowings_8D977989BB735B983270F3B0FD7D8EC1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermDebtCurrent" xlink:label="loc_us-gaap_LongTermDebtCurrent_97CDDEA300276A1AC660F3B0FD7D2546" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_F230E74D359EFE7BA52DF3B0FD7DB707" xlink:to="loc_us-gaap_LongTermDebtCurrent_97CDDEA300276A1AC660F3B0FD7D2546" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeLiabilitiesCurrent" xlink:label="loc_us-gaap_DerivativeLiabilitiesCurrent_2E1EBAC67FBB632660DCF3B0FD7D0CC7" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_F230E74D359EFE7BA52DF3B0FD7DB707" xlink:to="loc_us-gaap_DerivativeLiabilitiesCurrent_2E1EBAC67FBB632660DCF3B0FD7D0CC7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CustomerDepositsCurrent" xlink:label="loc_us-gaap_CustomerDepositsCurrent_3CD9A6230F2950AA22BCF3B0FD7D13BD" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_F230E74D359EFE7BA52DF3B0FD7DB707" xlink:to="loc_us-gaap_CustomerDepositsCurrent_3CD9A6230F2950AA22BCF3B0FD7D13BD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TaxesPayableCurrent" xlink:label="loc_us-gaap_TaxesPayableCurrent_642652C6BD7AEB8E1455F3B0FD7DBB2F" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_F230E74D359EFE7BA52DF3B0FD7DB707" xlink:to="loc_us-gaap_TaxesPayableCurrent_642652C6BD7AEB8E1455F3B0FD7DBB2F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InterestPayableCurrent" xlink:label="loc_us-gaap_InterestPayableCurrent_992A652979FD3D3CC4ECF3B0FD7D1AA8" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_F230E74D359EFE7BA52DF3B0FD7DB707" xlink:to="loc_us-gaap_InterestPayableCurrent_992A652979FD3D3CC4ECF3B0FD7D1AA8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CustomerRefundLiabilityCurrent" xlink:label="loc_us-gaap_CustomerRefundLiabilityCurrent_19009CC346A5C040E8CFF3B0FD7D12CE" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_F230E74D359EFE7BA52DF3B0FD7DB707" xlink:to="loc_us-gaap_CustomerRefundLiabilityCurrent_19009CC346A5C040E8CFF3B0FD7D12CE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CapitalLeaseObligationsCurrent" xlink:label="loc_us-gaap_CapitalLeaseObligationsCurrent_DD66DD5E4E805ED7E7D8F3B0FD7DBA7C" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_F230E74D359EFE7BA52DF3B0FD7DB707" xlink:to="loc_us-gaap_CapitalLeaseObligationsCurrent_DD66DD5E4E805ED7E7D8F3B0FD7DBA7C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RegulatoryLiabilityCurrent" xlink:label="loc_us-gaap_RegulatoryLiabilityCurrent_09C53FE4EAD6BCD6E462F3B0FD7D866E" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_F230E74D359EFE7BA52DF3B0FD7DB707" xlink:to="loc_us-gaap_RegulatoryLiabilityCurrent_09C53FE4EAD6BCD6E462F3B0FD7D866E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherLiabilitiesCurrent" xlink:label="loc_us-gaap_OtherLiabilitiesCurrent_F43C72672740FA645ED2F3B0FD7D1841" xlink:type="locator" />
    <link:definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_F230E74D359EFE7BA52DF3B0FD7DB707" xlink:to="loc_us-gaap_OtherLiabilitiesCurrent_F43C72672740FA645ED2F3B0FD7D1841" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LiabilitiesCurrent" xlink:label="loc_us-gaap_LiabilitiesCurrent_FE4788466050AC1FD056F3B0FD7DE85C" xlink:type="locator" />
    <link:definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_F230E74D359EFE7BA52DF3B0FD7DB707" xlink:to="loc_us-gaap_LiabilitiesCurrent_FE4788466050AC1FD056F3B0FD7DE85C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LiabilitiesNoncurrentAbstract" xlink:label="loc_us-gaap_LiabilitiesNoncurrentAbstract_D41EB9B09E0E6CED68DEF3B0FD7DA1C8" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9D4947F5977D7A467B1AF3B0FD7D02D1" xlink:to="loc_us-gaap_LiabilitiesNoncurrentAbstract_D41EB9B09E0E6CED68DEF3B0FD7DA1C8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermDebtNoncurrent" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_D9DE9FE7919ADE064227F3B0FD7D1F0C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_D41EB9B09E0E6CED68DEF3B0FD7DA1C8" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_D9DE9FE7919ADE064227F3B0FD7D1F0C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AffiliatedLongTermDebtNoncurrent" xlink:label="loc_aep_AffiliatedLongTermDebtNoncurrent_BADC7B1E10A510AD59C6F3B0FD7D33A3" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_D41EB9B09E0E6CED68DEF3B0FD7DA1C8" xlink:to="loc_aep_AffiliatedLongTermDebtNoncurrent_BADC7B1E10A510AD59C6F3B0FD7D33A3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeLiabilitiesNoncurrent" xlink:label="loc_us-gaap_DerivativeLiabilitiesNoncurrent_F013226D8DD784B972D2F3B0FD7D51D6" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_D41EB9B09E0E6CED68DEF3B0FD7DA1C8" xlink:to="loc_us-gaap_DerivativeLiabilitiesNoncurrent_F013226D8DD784B972D2F3B0FD7D51D6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredTaxLiabilitiesNoncurrent" xlink:label="loc_us-gaap_DeferredTaxLiabilitiesNoncurrent_F9A16C442F22512907ADF3B0FD7D72FB" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_D41EB9B09E0E6CED68DEF3B0FD7DA1C8" xlink:to="loc_us-gaap_DeferredTaxLiabilitiesNoncurrent_F9A16C442F22512907ADF3B0FD7D72FB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RegulatoryLiabilityNoncurrent" xlink:label="loc_us-gaap_RegulatoryLiabilityNoncurrent_57B0C0DE360F717D94A7F3B0FD7D8F57" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_D41EB9B09E0E6CED68DEF3B0FD7DA1C8" xlink:to="loc_us-gaap_RegulatoryLiabilityNoncurrent_57B0C0DE360F717D94A7F3B0FD7D8F57" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetRetirementObligationsNoncurrent" xlink:label="loc_us-gaap_AssetRetirementObligationsNoncurrent_F8610EE6728B56EAC7F0F3B0FD7D0B47" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_D41EB9B09E0E6CED68DEF3B0FD7DA1C8" xlink:to="loc_us-gaap_AssetRetirementObligationsNoncurrent_F8610EE6728B56EAC7F0F3B0FD7D0B47" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_EmployeeBenefitsAndPensionObligations" xlink:label="loc_aep_EmployeeBenefitsAndPensionObligations_A084FEB8B8B48AC3FB85F3B0FD7D2230" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_D41EB9B09E0E6CED68DEF3B0FD7DA1C8" xlink:to="loc_aep_EmployeeBenefitsAndPensionObligations_A084FEB8B8B48AC3FB85F3B0FD7D2230" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CapitalLeaseObligationsNoncurrent" xlink:label="loc_us-gaap_CapitalLeaseObligationsNoncurrent_2C4115C28061C13F9A1DF3B0FD7DB477" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_D41EB9B09E0E6CED68DEF3B0FD7DA1C8" xlink:to="loc_us-gaap_CapitalLeaseObligationsNoncurrent_2C4115C28061C13F9A1DF3B0FD7DB477" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OklaunionPurchasePowerAgreement" xlink:label="loc_aep_OklaunionPurchasePowerAgreement_DFF0F7CAD6F528FB06DAF3B0FD7D49E6" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_D41EB9B09E0E6CED68DEF3B0FD7DA1C8" xlink:to="loc_aep_OklaunionPurchasePowerAgreement_DFF0F7CAD6F528FB06DAF3B0FD7D49E6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherLiabilitiesNoncurrent" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_2167E42A1B92A24D6352F3B0FD7D0409" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_D41EB9B09E0E6CED68DEF3B0FD7DA1C8" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_2167E42A1B92A24D6352F3B0FD7D0409" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LiabilitiesNoncurrent" xlink:label="loc_us-gaap_LiabilitiesNoncurrent_A461C894C534284EC4DBF3B0FD7D324D" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_D41EB9B09E0E6CED68DEF3B0FD7DA1C8" xlink:to="loc_us-gaap_LiabilitiesNoncurrent_A461C894C534284EC4DBF3B0FD7D324D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Liabilities" xlink:label="loc_us-gaap_Liabilities_FE3FA70E1E52B19CF21DF3B0FD7DFFC1" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9D4947F5977D7A467B1AF3B0FD7D02D1" xlink:to="loc_us-gaap_Liabilities_FE3FA70E1E52B19CF21DF3B0FD7DFFC1" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RateMatters" xlink:label="loc_aep_RateMatters_8C0E3FCB2344DFFA3459F3B0FD7D5603" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9D4947F5977D7A467B1AF3B0FD7D02D1" xlink:to="loc_aep_RateMatters_8C0E3FCB2344DFFA3459F3B0FD7D5603" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommitmentsAndContingencies" xlink:label="loc_us-gaap_CommitmentsAndContingencies_15E2CF1B088894DE5AE3F3B0FD7D7E78" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9D4947F5977D7A467B1AF3B0FD7D02D1" xlink:to="loc_us-gaap_CommitmentsAndContingencies_15E2CF1B088894DE5AE3F3B0FD7D7E78" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount" xlink:label="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_7A56D240CDDADD638974F3B0FD7D42C0" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9D4947F5977D7A467B1AF3B0FD7D02D1" xlink:to="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_7A56D240CDDADD638974F3B0FD7D42C0" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ContingentlyRedeemablePerformanceShareAwards" xlink:label="loc_aep_ContingentlyRedeemablePerformanceShareAwards_B583070A8A20531A2B0AF3B0FD7DB279" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9D4947F5977D7A467B1AF3B0FD7D02D1" xlink:to="loc_aep_ContingentlyRedeemablePerformanceShareAwards_B583070A8A20531A2B0AF3B0FD7DB279" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_TotalMezzanineEquity" xlink:label="loc_aep_TotalMezzanineEquity_B1EDB52C6E7348AEBE8AF3B0FD7D0946" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9D4947F5977D7A467B1AF3B0FD7D02D1" xlink:to="loc_aep_TotalMezzanineEquity_B1EDB52C6E7348AEBE8AF3B0FD7D0946" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockholdersEquityAbstract" xlink:label="loc_us-gaap_StockholdersEquityAbstract_D5CED335CADBAAD1A8FAF3B0FD7D7474" xlink:type="locator" />
    <link:definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9D4947F5977D7A467B1AF3B0FD7D02D1" xlink:to="loc_us-gaap_StockholdersEquityAbstract_D5CED335CADBAAD1A8FAF3B0FD7D7474" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockValue" xlink:label="loc_us-gaap_CommonStockValue_219BAC99B3552A8BD6A1F3B0FD7DCD17" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_D5CED335CADBAAD1A8FAF3B0FD7D7474" xlink:to="loc_us-gaap_CommonStockValue_219BAC99B3552A8BD6A1F3B0FD7DCD17" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MembersCapital" xlink:label="loc_us-gaap_MembersCapital_B389441B7A79E32412BEF3B0FD8D48EC" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_D5CED335CADBAAD1A8FAF3B0FD7D7474" xlink:to="loc_us-gaap_MembersCapital_B389441B7A79E32412BEF3B0FD8D48EC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AdditionalPaidInCapital" xlink:label="loc_us-gaap_AdditionalPaidInCapital_A52C4AA74D79169E9BCEF3B0FD8DDBC8" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_D5CED335CADBAAD1A8FAF3B0FD7D7474" xlink:to="loc_us-gaap_AdditionalPaidInCapital_A52C4AA74D79169E9BCEF3B0FD8DDBC8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_DFC9406E52951B73BA6FF3B0FD8D325E" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_D5CED335CADBAAD1A8FAF3B0FD7D7474" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_DFC9406E52951B73BA6FF3B0FD8D325E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_15CBAB8A130463E73270F3B0FD8D72B1" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_D5CED335CADBAAD1A8FAF3B0FD7D7474" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_15CBAB8A130463E73270F3B0FD8D72B1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="loc_us-gaap_StockholdersEquity_5EF12050E8DD4522F190F3B0FD8D728D" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_D5CED335CADBAAD1A8FAF3B0FD7D7474" xlink:to="loc_us-gaap_StockholdersEquity_5EF12050E8DD4522F190F3B0FD8D728D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MinorityInterest" xlink:label="loc_us-gaap_MinorityInterest_65DD448A693A36932945F3B0FD8D97A5" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_D5CED335CADBAAD1A8FAF3B0FD7D7474" xlink:to="loc_us-gaap_MinorityInterest_65DD448A693A36932945F3B0FD8D97A5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_83D3E91090FD80538804F3B0FD8D6A25" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_D5CED335CADBAAD1A8FAF3B0FD7D7474" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_83D3E91090FD80538804F3B0FD8D6A25" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MembersEquity" xlink:label="loc_us-gaap_MembersEquity_7ABF44508F918B5C8767F3B0FD8D4470" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_D5CED335CADBAAD1A8FAF3B0FD7D7474" xlink:to="loc_us-gaap_MembersEquity_7ABF44508F918B5C8767F3B0FD8D4470" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_DFFAAEB3B3619B8C5A9BF3B0FD8DB395" xlink:type="locator" />
    <link:definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9D4947F5977D7A467B1AF3B0FD7D02D1" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_DFFAAEB3B3619B8C5A9BF3B0FD8DB395" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/CondensedConsolidatedBalanceSheetsParenthetical" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_DF1F2873A712F73AD7BCF7D1BD7110C2" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_C9EFAF28A32D400C3E8EF7D1BD676D7D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_DF1F2873A712F73AD7BCF7D1BD7110C2" xlink:to="loc_us-gaap_StatementTable_C9EFAF28A32D400C3E8EF7D1BD676D7D" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_F48589753D8D0944C9E0F7D1BD670B43" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_C9EFAF28A32D400C3E8EF7D1BD676D7D" xlink:to="loc_dei_LegalEntityAxis_F48589753D8D0944C9E0F7D1BD670B43" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_DDCFC61762FBEBE92E15F7D1BD67CA26_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_F48589753D8D0944C9E0F7D1BD670B43" xlink:to="loc_dei_EntityDomain_DDCFC61762FBEBE92E15F7D1BD67CA26_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_DDCFC61762FBEBE92E15F7D1BD67CA26" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_F48589753D8D0944C9E0F7D1BD670B43" xlink:to="loc_dei_EntityDomain_DDCFC61762FBEBE92E15F7D1BD67CA26" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTexasInc.Member" xlink:label="loc_aep_AEPTexasInc.Member_66F18BB432191D21615BF7D1BD672F86" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_DDCFC61762FBEBE92E15F7D1BD67CA26" xlink:to="loc_aep_AEPTexasInc.Member_66F18BB432191D21615BF7D1BD672F86" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTransmissionCoMember" xlink:label="loc_aep_AEPTransmissionCoMember_C6063435B1A193E4DEC0F7D1BD678071" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_DDCFC61762FBEBE92E15F7D1BD67CA26" xlink:to="loc_aep_AEPTransmissionCoMember_C6063435B1A193E4DEC0F7D1BD678071" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AppalachianPowerCoMember" xlink:label="loc_aep_AppalachianPowerCoMember_5653F44D6A3B6030AE05F7D1BD67F54B" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_DDCFC61762FBEBE92E15F7D1BD67CA26" xlink:to="loc_aep_AppalachianPowerCoMember_5653F44D6A3B6030AE05F7D1BD67F54B" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IndianaMichiganPowerCoMember" xlink:label="loc_aep_IndianaMichiganPowerCoMember_754D0C9F2610F1FA91F2F7D1BD6739A2" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_DDCFC61762FBEBE92E15F7D1BD67CA26" xlink:to="loc_aep_IndianaMichiganPowerCoMember_754D0C9F2610F1FA91F2F7D1BD6739A2" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OhioPowerCoMember" xlink:label="loc_aep_OhioPowerCoMember_FA9D228E9CA662FDE06CF7D1BD7166AC" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_DDCFC61762FBEBE92E15F7D1BD67CA26" xlink:to="loc_aep_OhioPowerCoMember_FA9D228E9CA662FDE06CF7D1BD7166AC" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_PublicServiceCoOfOklahomaMember" xlink:label="loc_aep_PublicServiceCoOfOklahomaMember_D83BDC38E14EFD5E4234F7D1BD71990F" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_DDCFC61762FBEBE92E15F7D1BD67CA26" xlink:to="loc_aep_PublicServiceCoOfOklahomaMember_D83BDC38E14EFD5E4234F7D1BD71990F" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SouthwesternElectricPowerCoMember" xlink:label="loc_aep_SouthwesternElectricPowerCoMember_625C6E925919DEB2042AF7D1BD7197CC" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_DDCFC61762FBEBE92E15F7D1BD67CA26" xlink:to="loc_aep_SouthwesternElectricPowerCoMember_625C6E925919DEB2042AF7D1BD7197CC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesAxis" xlink:label="loc_us-gaap_ConsolidatedEntitiesAxis_B0EA06EBAF7340B28E57F7D1BD711ECA" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_C9EFAF28A32D400C3E8EF7D1BD676D7D" xlink:to="loc_us-gaap_ConsolidatedEntitiesAxis_B0EA06EBAF7340B28E57F7D1BD711ECA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesDomain" xlink:label="loc_us-gaap_ConsolidatedEntitiesDomain_099ED7F947E83381DD65F7D1BD71F02B_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConsolidatedEntitiesAxis_B0EA06EBAF7340B28E57F7D1BD711ECA" xlink:to="loc_us-gaap_ConsolidatedEntitiesDomain_099ED7F947E83381DD65F7D1BD71F02B_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesDomain" xlink:label="loc_us-gaap_ConsolidatedEntitiesDomain_099ED7F947E83381DD65F7D1BD71F02B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConsolidatedEntitiesAxis_B0EA06EBAF7340B28E57F7D1BD711ECA" xlink:to="loc_us-gaap_ConsolidatedEntitiesDomain_099ED7F947E83381DD65F7D1BD71F02B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsidiariesMember" xlink:label="loc_us-gaap_SubsidiariesMember_CAA59DA18826C9AF821AF7D1BD719055" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidatedEntitiesDomain_099ED7F947E83381DD65F7D1BD71F02B" xlink:to="loc_us-gaap_SubsidiariesMember_CAA59DA18826C9AF821AF7D1BD719055" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis" xlink:label="loc_us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis_2A0F6DB265BC55634D45F7D1BD715DE9" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_C9EFAF28A32D400C3E8EF7D1BD676D7D" xlink:to="loc_us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis_2A0F6DB265BC55634D45F7D1BD715DE9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassificationOfVariableInterestEntityDomain" xlink:label="loc_us-gaap_ClassificationOfVariableInterestEntityDomain_2E7385C2F3C4EC31C9F9F7D1BD7152D0_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis_2A0F6DB265BC55634D45F7D1BD715DE9" xlink:to="loc_us-gaap_ClassificationOfVariableInterestEntityDomain_2E7385C2F3C4EC31C9F9F7D1BD7152D0_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassificationOfVariableInterestEntityDomain" xlink:label="loc_us-gaap_ClassificationOfVariableInterestEntityDomain_2E7385C2F3C4EC31C9F9F7D1BD7152D0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis_2A0F6DB265BC55634D45F7D1BD715DE9" xlink:to="loc_us-gaap_ClassificationOfVariableInterestEntityDomain_2E7385C2F3C4EC31C9F9F7D1BD7152D0" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AepTexasCentralTransitionFundingCoMember" xlink:label="loc_aep_AepTexasCentralTransitionFundingCoMember_5A3347B360ACEDB0C825F7D1BD716A7D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassificationOfVariableInterestEntityDomain_2E7385C2F3C4EC31C9F9F7D1BD7152D0" xlink:to="loc_aep_AepTexasCentralTransitionFundingCoMember_5A3347B360ACEDB0C825F7D1BD716A7D" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OhioPhaseInRecoveryFundingMember" xlink:label="loc_aep_OhioPhaseInRecoveryFundingMember_815145D3B86A1C0ADAC1F7D1BD7195E8" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassificationOfVariableInterestEntityDomain_2E7385C2F3C4EC31C9F9F7D1BD7152D0" xlink:to="loc_aep_OhioPhaseInRecoveryFundingMember_815145D3B86A1C0ADAC1F7D1BD7195E8" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SabineMiningCoMember" xlink:label="loc_aep_SabineMiningCoMember_4B9A73B35E304CD1EC0EF7D1BD71B10F" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassificationOfVariableInterestEntityDomain_2E7385C2F3C4EC31C9F9F7D1BD7152D0" xlink:to="loc_aep_SabineMiningCoMember_4B9A73B35E304CD1EC0EF7D1BD71B10F" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_DccFuelMember" xlink:label="loc_aep_DccFuelMember_135E06FF85C6D6AF3A96F7D1BD718E73" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassificationOfVariableInterestEntityDomain_2E7385C2F3C4EC31C9F9F7D1BD7152D0" xlink:to="loc_aep_DccFuelMember_135E06FF85C6D6AF3A96F7D1BD718E73" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetsCurrentAbstract" xlink:label="loc_us-gaap_AssetsCurrentAbstract_D88F684EF9C370E386EDF7D1BD71DF49" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_DF1F2873A712F73AD7BCF7D1BD7110C2" xlink:to="loc_us-gaap_AssetsCurrentAbstract_D88F684EF9C370E386EDF7D1BD71DF49" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_EDBFA4925FE023211401F7D1BD717BD8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_D88F684EF9C370E386EDF7D1BD71DF49" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_EDBFA4925FE023211401F7D1BD717BD8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue_4468F4E3511DE46F43E7F7D1BD712B3F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_D88F684EF9C370E386EDF7D1BD71DF49" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue_4468F4E3511DE46F43E7F7D1BD712B3F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShortTermInvestments" xlink:label="loc_us-gaap_ShortTermInvestments_F3EB5D798B375C267AACF7D1BD71A2A7" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_D88F684EF9C370E386EDF7D1BD71DF49" xlink:to="loc_us-gaap_ShortTermInvestments_F3EB5D798B375C267AACF7D1BD71A2A7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InventoryRawMaterials" xlink:label="loc_us-gaap_InventoryRawMaterials_ABF56C7B514BC057433FF7D1BD715B31" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_D88F684EF9C370E386EDF7D1BD71DF49" xlink:to="loc_us-gaap_InventoryRawMaterials_ABF56C7B514BC057433FF7D1BD715B31" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentGrossAbstract" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGrossAbstract_8CBD5C4A1D4A654930D5F7D1BD7127DC" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_DF1F2873A712F73AD7BCF7D1BD7110C2" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGrossAbstract_8CBD5C4A1D4A654930D5F7D1BD7127DC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PublicUtilitiesPropertyPlantAndEquipmentOtherPropertyPlantAndEquipment" xlink:label="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentOtherPropertyPlantAndEquipment_4BD03026F309C0E338FCF7D1BD71D98B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentGrossAbstract_8CBD5C4A1D4A654930D5F7D1BD7127DC" xlink:to="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentOtherPropertyPlantAndEquipment_4BD03026F309C0E338FCF7D1BD71D98B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_E7A1DC8DBE2591904B5CF7D1BD716CA6" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentGrossAbstract_8CBD5C4A1D4A654930D5F7D1BD7127DC" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_E7A1DC8DBE2591904B5CF7D1BD716CA6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetsNoncurrentAbstract" xlink:label="loc_us-gaap_AssetsNoncurrentAbstract_7927C14037F952EB6913F7D1BD71C6B2" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_DF1F2873A712F73AD7BCF7D1BD7110C2" xlink:to="loc_us-gaap_AssetsNoncurrentAbstract_7927C14037F952EB6913F7D1BD71C6B2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SecuritizedRegulatoryTransitionAssetsNoncurrent" xlink:label="loc_us-gaap_SecuritizedRegulatoryTransitionAssetsNoncurrent_07F5E5706344D6CF12DEF7D1BD7126F1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_7927C14037F952EB6913F7D1BD71C6B2" xlink:to="loc_us-gaap_SecuritizedRegulatoryTransitionAssetsNoncurrent_07F5E5706344D6CF12DEF7D1BD7126F1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LiabilitiesCurrentAbstract" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_B1C8D5D6C394BBF655FCF7D1BD71EFF6" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_DF1F2873A712F73AD7BCF7D1BD7110C2" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_B1C8D5D6C394BBF655FCF7D1BD71EFF6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermDebtCurrent" xlink:label="loc_us-gaap_LongTermDebtCurrent_74208CD6A7ED736CA6E7F7D1BD71313C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_B1C8D5D6C394BBF655FCF7D1BD71EFF6" xlink:to="loc_us-gaap_LongTermDebtCurrent_74208CD6A7ED736CA6E7F7D1BD71313C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InterestPayableCurrent" xlink:label="loc_us-gaap_InterestPayableCurrent_327FC3C593973C64441AF7D1BD71630A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_B1C8D5D6C394BBF655FCF7D1BD71EFF6" xlink:to="loc_us-gaap_InterestPayableCurrent_327FC3C593973C64441AF7D1BD71630A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LiabilitiesNoncurrentAbstract" xlink:label="loc_us-gaap_LiabilitiesNoncurrentAbstract_04E8F4920292077F9F92F7D1BD714C5A" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_DF1F2873A712F73AD7BCF7D1BD7110C2" xlink:to="loc_us-gaap_LiabilitiesNoncurrentAbstract_04E8F4920292077F9F92F7D1BD714C5A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermDebtNoncurrent" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_4B605F8571D16512C919F7D1BD71E3BB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_04E8F4920292077F9F92F7D1BD714C5A" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_4B605F8571D16512C919F7D1BD71E3BB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockholdersEquityAbstract" xlink:label="loc_us-gaap_StockholdersEquityAbstract_82F83F41A680AF3731AFF7D1BD715E3F" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_DF1F2873A712F73AD7BCF7D1BD7110C2" xlink:to="loc_us-gaap_StockholdersEquityAbstract_82F83F41A680AF3731AFF7D1BD715E3F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockNoParValue" xlink:label="loc_us-gaap_CommonStockNoParValue_075C188821D28C0DC5C1F7D1BD7116C0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_82F83F41A680AF3731AFF7D1BD715E3F" xlink:to="loc_us-gaap_CommonStockNoParValue_075C188821D28C0DC5C1F7D1BD7116C0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_2FA27579544D398BE68DF7D1BD710623" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_82F83F41A680AF3731AFF7D1BD715E3F" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_2FA27579544D398BE68DF7D1BD710623" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_389CBA9B37E63B4BF1C0F7D1BD718CEA" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_82F83F41A680AF3731AFF7D1BD715E3F" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_389CBA9B37E63B4BF1C0F7D1BD718CEA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockSharesIssued" xlink:label="loc_us-gaap_CommonStockSharesIssued_3A625946AB48AFA6CA5AF7D1BD71544C" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_82F83F41A680AF3731AFF7D1BD715E3F" xlink:to="loc_us-gaap_CommonStockSharesIssued_3A625946AB48AFA6CA5AF7D1BD71544C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_BB39BAD6ADEA0E359292F7D1BD71CADA" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_82F83F41A680AF3731AFF7D1BD715E3F" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_BB39BAD6ADEA0E359292F7D1BD71CADA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TreasuryStockShares" xlink:label="loc_us-gaap_TreasuryStockShares_3C973B3CDC2509AB1F25F7D1BD713CD3" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_82F83F41A680AF3731AFF7D1BD715E3F" xlink:to="loc_us-gaap_TreasuryStockShares_3C973B3CDC2509AB1F25F7D1BD713CD3" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/CondensedConsolidatedStatementsOfCashFlows" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_6349D1B5FA02A98EDFDDF7E159E25C58" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_D6558B31B209254DA13EF7E159E2F1B4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_6349D1B5FA02A98EDFDDF7E159E25C58" xlink:to="loc_us-gaap_StatementTable_D6558B31B209254DA13EF7E159E2F1B4" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_D17818AC3AC9DF68412AF7E159E2DBD0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_D6558B31B209254DA13EF7E159E2F1B4" xlink:to="loc_dei_LegalEntityAxis_D17818AC3AC9DF68412AF7E159E2DBD0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_B69755E8B8EEB5D852F7F7E159E2E703_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_D17818AC3AC9DF68412AF7E159E2DBD0" xlink:to="loc_dei_EntityDomain_B69755E8B8EEB5D852F7F7E159E2E703_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_B69755E8B8EEB5D852F7F7E159E2E703" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_D17818AC3AC9DF68412AF7E159E2DBD0" xlink:to="loc_dei_EntityDomain_B69755E8B8EEB5D852F7F7E159E2E703" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTexasInc.Member" xlink:label="loc_aep_AEPTexasInc.Member_92441EB1B595190E5060F7E159E22B38" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_B69755E8B8EEB5D852F7F7E159E2E703" xlink:to="loc_aep_AEPTexasInc.Member_92441EB1B595190E5060F7E159E22B38" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTransmissionCoMember" xlink:label="loc_aep_AEPTransmissionCoMember_4918FFA62BF588E6932DF7E159E2DD21" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_B69755E8B8EEB5D852F7F7E159E2E703" xlink:to="loc_aep_AEPTransmissionCoMember_4918FFA62BF588E6932DF7E159E2DD21" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AppalachianPowerCoMember" xlink:label="loc_aep_AppalachianPowerCoMember_29F59A4036AE25C62C3DF7E159E2362F" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_B69755E8B8EEB5D852F7F7E159E2E703" xlink:to="loc_aep_AppalachianPowerCoMember_29F59A4036AE25C62C3DF7E159E2362F" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IndianaMichiganPowerCoMember" xlink:label="loc_aep_IndianaMichiganPowerCoMember_4BD0F59AF01C076E3FC2F7E159E24E37" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_B69755E8B8EEB5D852F7F7E159E2E703" xlink:to="loc_aep_IndianaMichiganPowerCoMember_4BD0F59AF01C076E3FC2F7E159E24E37" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OhioPowerCoMember" xlink:label="loc_aep_OhioPowerCoMember_33206F2823D199364CA1F7E159E2B169" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_B69755E8B8EEB5D852F7F7E159E2E703" xlink:to="loc_aep_OhioPowerCoMember_33206F2823D199364CA1F7E159E2B169" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_PublicServiceCoOfOklahomaMember" xlink:label="loc_aep_PublicServiceCoOfOklahomaMember_69EA7137A4724D01D79EF7E159E29CF7" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_B69755E8B8EEB5D852F7F7E159E2E703" xlink:to="loc_aep_PublicServiceCoOfOklahomaMember_69EA7137A4724D01D79EF7E159E29CF7" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SouthwesternElectricPowerCoMember" xlink:label="loc_aep_SouthwesternElectricPowerCoMember_3A9BDFBCE7BE6F42D9E7F7E159E27F5E" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_B69755E8B8EEB5D852F7F7E159E2E703" xlink:to="loc_aep_SouthwesternElectricPowerCoMember_3A9BDFBCE7BE6F42D9E7F7E159E27F5E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_E8ADB470BBC18264B30EF7E159E2216D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_6349D1B5FA02A98EDFDDF7E159E25C58" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_E8ADB470BBC18264B30EF7E159E2216D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProfitLoss" xlink:label="loc_us-gaap_ProfitLoss_440E07345DF136425B9FF7E159E29191" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_E8ADB470BBC18264B30EF7E159E2216D" xlink:to="loc_us-gaap_ProfitLoss_440E07345DF136425B9FF7E159E29191" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_751BFC84F45184F142EDF7E159E2E500" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_E8ADB470BBC18264B30EF7E159E2216D" xlink:to="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_751BFC84F45184F142EDF7E159E2E500" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_UtilitiesOperatingExpenseDepreciationAndAmortization" xlink:label="loc_us-gaap_UtilitiesOperatingExpenseDepreciationAndAmortization_973F41CFABFAB548EBBAF7E159E2BB70" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_751BFC84F45184F142EDF7E159E2E500" xlink:to="loc_us-gaap_UtilitiesOperatingExpenseDepreciationAndAmortization_973F41CFABFAB548EBBAF7E159E2BB70" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AmortizationOfGenerationDeferrals" xlink:label="loc_aep_AmortizationOfGenerationDeferrals_4D1CD12C043611B4FE63F7E159E2E15A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_751BFC84F45184F142EDF7E159E2E500" xlink:to="loc_aep_AmortizationOfGenerationDeferrals_4D1CD12C043611B4FE63F7E159E2E15A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredIncomeTaxExpenseBenefit" xlink:label="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_B159C0EF6265602E4DD7F7E159E20C8C" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_751BFC84F45184F142EDF7E159E2E500" xlink:to="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_B159C0EF6265602E4DD7F7E159E20C8C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_DeferralOfIncrementalNuclearRefuelingOutageExpensesNet" xlink:label="loc_aep_DeferralOfIncrementalNuclearRefuelingOutageExpensesNet_528313144F895FA445BDF7E159E24F64" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_751BFC84F45184F142EDF7E159E2E500" xlink:to="loc_aep_DeferralOfIncrementalNuclearRefuelingOutageExpensesNet_528313144F895FA445BDF7E159E24F64" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_CarryingCostsIncome" xlink:label="loc_aep_CarryingCostsIncome_22A32C64A3F93734E4E3F7E159E239BD" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_751BFC84F45184F142EDF7E159E2E500" xlink:to="loc_aep_CarryingCostsIncome_22A32C64A3F93734E4E3F7E159E239BD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity" xlink:label="loc_us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity_24E296916EF997C5B2D4F7E159E27463" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_751BFC84F45184F142EDF7E159E2E500" xlink:to="loc_us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity_24E296916EF997C5B2D4F7E159E27463" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_UnrealizedGainLossOnDerivatives" xlink:label="loc_us-gaap_UnrealizedGainLossOnDerivatives_8416E9094BCE355C4456F7E159E27BEA" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_751BFC84F45184F142EDF7E159E2E500" xlink:to="loc_us-gaap_UnrealizedGainLossOnDerivatives_8416E9094BCE355C4456F7E159E27BEA" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AmortizationOfNuclearFuel" xlink:label="loc_aep_AmortizationOfNuclearFuel_554C5ED792A7B3E9CACBF7E159E2A3B3" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_751BFC84F45184F142EDF7E159E2E500" xlink:to="loc_aep_AmortizationOfNuclearFuel_554C5ED792A7B3E9CACBF7E159E2A3B3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AmortizationOfDeferredPropertyTaxes" xlink:label="loc_us-gaap_AmortizationOfDeferredPropertyTaxes_29C2E480FFFA9BE128C0F7E159E2CD8F" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_751BFC84F45184F142EDF7E159E2E500" xlink:to="loc_us-gaap_AmortizationOfDeferredPropertyTaxes_29C2E480FFFA9BE128C0F7E159E2CD8F" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_FuelOverUnderRecoveryNet" xlink:label="loc_aep_FuelOverUnderRecoveryNet_63D25A4FAC5E40E95401F7E159E253C3" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_751BFC84F45184F142EDF7E159E2E500" xlink:to="loc_aep_FuelOverUnderRecoveryNet_63D25A4FAC5E40E95401F7E159E253C3" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_GainonSaleofMerchantGenerationAssets" xlink:label="loc_aep_GainonSaleofMerchantGenerationAssets_971D3709F38B7C594C5AF7E159E219BE" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_751BFC84F45184F142EDF7E159E2E500" xlink:to="loc_aep_GainonSaleofMerchantGenerationAssets_971D3709F38B7C594C5AF7E159E219BE" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ProvisionforRefund" xlink:label="loc_aep_ProvisionforRefund_88D3077CE958D06839B9F7E159E2328D" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_751BFC84F45184F142EDF7E159E2E500" xlink:to="loc_aep_ProvisionforRefund_88D3077CE958D06839B9F7E159E2328D" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_DeferralOfOhioCapacityCosts" xlink:label="loc_aep_DeferralOfOhioCapacityCosts_6CA79501D759D3AD05E2F7E159E2C6A6" xlink:type="locator" />
    <link:definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_751BFC84F45184F142EDF7E159E2E500" xlink:to="loc_aep_DeferralOfOhioCapacityCosts_6CA79501D759D3AD05E2F7E159E2C6A6" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ProvisionforRefundGlobalSettlement" xlink:label="loc_aep_ProvisionforRefundGlobalSettlement_F1FF679CB6B73EC7D309F7E159E2B322" xlink:type="locator" />
    <link:definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_751BFC84F45184F142EDF7E159E2E500" xlink:to="loc_aep_ProvisionforRefundGlobalSettlement_F1FF679CB6B73EC7D309F7E159E2B322" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncreaseDecreaseInOtherNoncurrentAssets" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherNoncurrentAssets_BA43AEF63A0BF3ED3A37F7E159E2BC10" xlink:type="locator" />
    <link:definitionArc order="15" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_751BFC84F45184F142EDF7E159E2E500" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherNoncurrentAssets_BA43AEF63A0BF3ED3A37F7E159E2BC10" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncreaseDecreaseInOtherNoncurrentLiabilities" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherNoncurrentLiabilities_DC3BAE42A7A8E9EB4A4DF7E159E21D1D" xlink:type="locator" />
    <link:definitionArc order="16" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_751BFC84F45184F142EDF7E159E2E500" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherNoncurrentLiabilities_DC3BAE42A7A8E9EB4A4DF7E159E21D1D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_00C28793B84A905CC872F7E159E242C3" xlink:type="locator" />
    <link:definitionArc order="17" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_751BFC84F45184F142EDF7E159E2E500" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_00C28793B84A905CC872F7E159E242C3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncreaseDecreaseInAccountsAndOtherReceivables" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsAndOtherReceivables_0BD608DE22CDBD1CDA9CF7E159E2D773" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_00C28793B84A905CC872F7E159E242C3" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsAndOtherReceivables_0BD608DE22CDBD1CDA9CF7E159E2D773" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncreaseDecreaseInInventories" xlink:label="loc_us-gaap_IncreaseDecreaseInInventories_BCBA372DA8333FEDB32BF7E159E2CD12" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_00C28793B84A905CC872F7E159E242C3" xlink:to="loc_us-gaap_IncreaseDecreaseInInventories_BCBA372DA8333FEDB32BF7E159E2CD12" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncreaseDecreaseInAccountsPayable" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsPayable_074C23D8668D5BD5EB92F7E159E2D328" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_00C28793B84A905CC872F7E159E242C3" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsPayable_074C23D8668D5BD5EB92F7E159E2D328" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncreaseDecreaseInAccruedTaxesPayable" xlink:label="loc_us-gaap_IncreaseDecreaseInAccruedTaxesPayable_5F5DFE7A175797AFBEBDF7E159E27EF7" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_00C28793B84A905CC872F7E159E242C3" xlink:to="loc_us-gaap_IncreaseDecreaseInAccruedTaxesPayable_5F5DFE7A175797AFBEBDF7E159E27EF7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncreaseDecreaseInInterestPayableNet" xlink:label="loc_us-gaap_IncreaseDecreaseInInterestPayableNet_FA740AD200845C7A2245F7E159E29BD9" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_00C28793B84A905CC872F7E159E242C3" xlink:to="loc_us-gaap_IncreaseDecreaseInInterestPayableNet_FA740AD200845C7A2245F7E159E29BD9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncreaseDecreaseInOtherCurrentAssets" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherCurrentAssets_7C62CB199CD79424FBFBF7E159E2CE84" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_00C28793B84A905CC872F7E159E242C3" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherCurrentAssets_7C62CB199CD79424FBFBF7E159E2CE84" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncreaseDecreaseInOtherCurrentLiabilities" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherCurrentLiabilities_34A8DF2FCCE2503C033FF7E159E279A7" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_00C28793B84A905CC872F7E159E242C3" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherCurrentLiabilities_34A8DF2FCCE2503C033FF7E159E279A7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_887BB55C1D4C1060487DF7E159E2B5AF" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_6349D1B5FA02A98EDFDDF7E159E25C58" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_887BB55C1D4C1060487DF7E159E2B5AF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_55799DEA6B74B05CAA3EF7E159E2090A" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_6349D1B5FA02A98EDFDDF7E159E25C58" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_55799DEA6B74B05CAA3EF7E159E2090A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsForConstructionInProcess" xlink:label="loc_us-gaap_PaymentsForConstructionInProcess_569F97FCB51F2A2C2048F7E159E2F6EE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_55799DEA6B74B05CAA3EF7E159E2090A" xlink:to="loc_us-gaap_PaymentsForConstructionInProcess_569F97FCB51F2A2C2048F7E159E2F6EE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncreaseDecreaseInNotesReceivableRelatedParties" xlink:label="loc_us-gaap_IncreaseDecreaseInNotesReceivableRelatedParties_1EFA29FBC42491E8D032F7E159E2E9FA" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_55799DEA6B74B05CAA3EF7E159E2090A" xlink:to="loc_us-gaap_IncreaseDecreaseInNotesReceivableRelatedParties_1EFA29FBC42491E8D032F7E159E2E9FA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsToAcquireInvestments" xlink:label="loc_us-gaap_PaymentsToAcquireInvestments_96C1A05D46C0A7BE6529F7E159E26AE4" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_55799DEA6B74B05CAA3EF7E159E2090A" xlink:to="loc_us-gaap_PaymentsToAcquireInvestments_96C1A05D46C0A7BE6529F7E159E26AE4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromSaleMaturityAndCollectionsOfInvestments" xlink:label="loc_us-gaap_ProceedsFromSaleMaturityAndCollectionsOfInvestments_6CFD1E880921E205AA7DF7E159E2B307" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_55799DEA6B74B05CAA3EF7E159E2090A" xlink:to="loc_us-gaap_ProceedsFromSaleMaturityAndCollectionsOfInvestments_6CFD1E880921E205AA7DF7E159E2B307" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsForNuclearFuel" xlink:label="loc_us-gaap_PaymentsForNuclearFuel_BE6D1D2FFEC84A1F3D31F7E159E25D9D" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_55799DEA6B74B05CAA3EF7E159E2090A" xlink:to="loc_us-gaap_PaymentsForNuclearFuel_BE6D1D2FFEC84A1F3D31F7E159E25D9D" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_Aep_ProceedsFromSaleOfMerchantGenerationAssets" xlink:label="loc_aep_Aep_ProceedsFromSaleOfMerchantGenerationAssets_C333A2A213EA51A0A8FBF7E159E2FCB7" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_55799DEA6B74B05CAA3EF7E159E2090A" xlink:to="loc_aep_Aep_ProceedsFromSaleOfMerchantGenerationAssets_C333A2A213EA51A0A8FBF7E159E2FCB7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_F82C6B9D5D08CFD13409F7E159E2C473" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_55799DEA6B74B05CAA3EF7E159E2090A" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_F82C6B9D5D08CFD13409F7E159E2C473" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsForProceedsFromOtherInvestingActivities" xlink:label="loc_us-gaap_PaymentsForProceedsFromOtherInvestingActivities_2A77C445DB0A8F35EE56F7E159E28E43" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_55799DEA6B74B05CAA3EF7E159E2090A" xlink:to="loc_us-gaap_PaymentsForProceedsFromOtherInvestingActivities_2A77C445DB0A8F35EE56F7E159E28E43" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_B2A5103346D095F94A8CF7E159E2183B" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_55799DEA6B74B05CAA3EF7E159E2090A" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_B2A5103346D095F94A8CF7E159E2183B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_F4A0F344EFE30FECAFB3F7E159E2F799" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_6349D1B5FA02A98EDFDDF7E159E25C58" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_F4A0F344EFE30FECAFB3F7E159E2F799" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromContributionsFromParent" xlink:label="loc_us-gaap_ProceedsFromContributionsFromParent_B94B640FEABD09C17210F7E159E2D6C5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_F4A0F344EFE30FECAFB3F7E159E2F799" xlink:to="loc_us-gaap_ProceedsFromContributionsFromParent_B94B640FEABD09C17210F7E159E2D6C5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_DF3A97CC6C7A11780C7FF7E159E26F0B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_F4A0F344EFE30FECAFB3F7E159E2F799" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_DF3A97CC6C7A11780C7FF7E159E26F0B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromIssuanceOfLongTermDebt" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_80A3E0603900C7A9F841F7E159E2B4A5" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_F4A0F344EFE30FECAFB3F7E159E2F799" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_80A3E0603900C7A9F841F7E159E2B4A5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromShortTermDebtMaturingInMoreThanThreeMonths" xlink:label="loc_us-gaap_ProceedsFromShortTermDebtMaturingInMoreThanThreeMonths_67A6066A5B63C21239F5F7E159E24991" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_F4A0F344EFE30FECAFB3F7E159E2F799" xlink:to="loc_us-gaap_ProceedsFromShortTermDebtMaturingInMoreThanThreeMonths_67A6066A5B63C21239F5F7E159E24991" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromRepaymentsOfShortTermDebtMaturingInThreeMonthsOrLess" xlink:label="loc_us-gaap_ProceedsFromRepaymentsOfShortTermDebtMaturingInThreeMonthsOrLess_E66A282756720E58BEC1F7E159E2C1D7" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_F4A0F344EFE30FECAFB3F7E159E2F799" xlink:to="loc_us-gaap_ProceedsFromRepaymentsOfShortTermDebtMaturingInThreeMonthsOrLess_E66A282756720E58BEC1F7E159E2C1D7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncreaseDecreaseInNotesPayableRelatedParties" xlink:label="loc_us-gaap_IncreaseDecreaseInNotesPayableRelatedParties_22393F990E52AB85C103F7E159E275C6" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_F4A0F344EFE30FECAFB3F7E159E2F799" xlink:to="loc_us-gaap_IncreaseDecreaseInNotesPayableRelatedParties_22393F990E52AB85C103F7E159E275C6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RepaymentsOfLongTermDebt" xlink:label="loc_us-gaap_RepaymentsOfLongTermDebt_B76E490B2079A97AEA37F7E159E2B88F" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_F4A0F344EFE30FECAFB3F7E159E2F799" xlink:to="loc_us-gaap_RepaymentsOfLongTermDebt_B76E490B2079A97AEA37F7E159E2B88F" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MakeWholePremiumonExtinguishmentofLongtermDebt" xlink:label="loc_aep_MakeWholePremiumonExtinguishmentofLongtermDebt_DFDF8D2C98C8651AB5B5F7E159E2B5AE" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_F4A0F344EFE30FECAFB3F7E159E2F799" xlink:to="loc_aep_MakeWholePremiumonExtinguishmentofLongtermDebt_DFDF8D2C98C8651AB5B5F7E159E2B5AE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RepaymentsOfLongTermCapitalLeaseObligations" xlink:label="loc_us-gaap_RepaymentsOfLongTermCapitalLeaseObligations_6CBB9E9CE15109841617F7E159E2BC34" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_F4A0F344EFE30FECAFB3F7E159E2F799" xlink:to="loc_us-gaap_RepaymentsOfLongTermCapitalLeaseObligations_6CBB9E9CE15109841617F7E159E2BC34" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsOfDistributionsToAffiliates" xlink:label="loc_us-gaap_PaymentsOfDistributionsToAffiliates_49958C78207907D36ADFF7E159E2E57F" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_F4A0F344EFE30FECAFB3F7E159E2F799" xlink:to="loc_us-gaap_PaymentsOfDistributionsToAffiliates_49958C78207907D36ADFF7E159E2E57F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsOfDividendsCommonStock" xlink:label="loc_us-gaap_PaymentsOfDividendsCommonStock_58D75FCE5215E6690825F7E159E25140" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_F4A0F344EFE30FECAFB3F7E159E2F799" xlink:to="loc_us-gaap_PaymentsOfDividendsCommonStock_58D75FCE5215E6690825F7E159E25140" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromPaymentsForOtherFinancingActivities" xlink:label="loc_us-gaap_ProceedsFromPaymentsForOtherFinancingActivities_CE2333D5827591AFABBEF7E159E27282" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_F4A0F344EFE30FECAFB3F7E159E2F799" xlink:to="loc_us-gaap_ProceedsFromPaymentsForOtherFinancingActivities_CE2333D5827591AFABBEF7E159E27282" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_5E1AAF8A78799314B422F7E159E23F19" xlink:type="locator" />
    <link:definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_F4A0F344EFE30FECAFB3F7E159E2F799" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_5E1AAF8A78799314B422F7E159E23F19" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect_046BED6CAE475F84AD2AF7E159E226DE" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_6349D1B5FA02A98EDFDDF7E159E25C58" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect_046BED6CAE475F84AD2AF7E159E226DE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" xlink:label="loc_us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_DB564EFE8C9144AC6DA8F7E159E291DA" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_6349D1B5FA02A98EDFDDF7E159E25C58" xlink:to="loc_us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_DB564EFE8C9144AC6DA8F7E159E291DA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_BC505F19E7A2FD9AB4F9F7E159E25413" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_6349D1B5FA02A98EDFDDF7E159E25C58" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_BC505F19E7A2FD9AB4F9F7E159E25413" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_673B42AE3BC064664012F7E159E28B6F" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_6349D1B5FA02A98EDFDDF7E159E25C58" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_673B42AE3BC064664012F7E159E28B6F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SupplementalCashFlowInformationAbstract" xlink:label="loc_us-gaap_SupplementalCashFlowInformationAbstract_101060440EAE04E40FC5F7E159E28F22" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_6349D1B5FA02A98EDFDDF7E159E25C58" xlink:to="loc_us-gaap_SupplementalCashFlowInformationAbstract_101060440EAE04E40FC5F7E159E28F22" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InterestPaidNet" xlink:label="loc_us-gaap_InterestPaidNet_542C7300CAF083D4123FF7E159E2B3DB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_101060440EAE04E40FC5F7E159E28F22" xlink:to="loc_us-gaap_InterestPaidNet_542C7300CAF083D4123FF7E159E2B3DB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeTaxesPaidNet" xlink:label="loc_us-gaap_IncomeTaxesPaidNet_4076CEA4F40941281496F7E159E25C94" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_101060440EAE04E40FC5F7E159E28F22" xlink:to="loc_us-gaap_IncomeTaxesPaidNet_4076CEA4F40941281496F7E159E25C94" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CapitalLeaseObligationsIncurred" xlink:label="loc_us-gaap_CapitalLeaseObligationsIncurred_77AA45C270FF5F53AE93F7E159E2FC07" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_101060440EAE04E40FC5F7E159E28F22" xlink:to="loc_us-gaap_CapitalLeaseObligationsIncurred_77AA45C270FF5F53AE93F7E159E2FC07" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConstructionInProgressExpendituresIncurredButNotYetPaid" xlink:label="loc_us-gaap_ConstructionInProgressExpendituresIncurredButNotYetPaid_100D842C48A338A763F6F7E159E2DF23" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_101060440EAE04E40FC5F7E159E28F22" xlink:to="loc_us-gaap_ConstructionInProgressExpendituresIncurredButNotYetPaid_100D842C48A338A763F6F7E159E2DF23" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AcquisitionOfNuclearFuelIncludedInCurrentLiabilities" xlink:label="loc_aep_AcquisitionOfNuclearFuelIncludedInCurrentLiabilities_26169C96F3947EE7EA81F7E159E26879" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_101060440EAE04E40FC5F7E159E28F22" xlink:to="loc_aep_AcquisitionOfNuclearFuelIncludedInCurrentLiabilities_26169C96F3947EE7EA81F7E159E26879" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NoncashOrPartNoncashAcquisitionInvestmentsAcquired1" xlink:label="loc_us-gaap_NoncashOrPartNoncashAcquisitionInvestmentsAcquired1_EED9F59607A711C562F0F7E159E2BE50" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_101060440EAE04E40FC5F7E159E28F22" xlink:to="loc_us-gaap_NoncashOrPartNoncashAcquisitionInvestmentsAcquired1_EED9F59607A711C562F0F7E159E2BE50" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ExpectedReimbursementForSpentNuclearFuelDryCaskStorage" xlink:label="loc_aep_ExpectedReimbursementForSpentNuclearFuelDryCaskStorage_EDD8A78C0D42F7491454F7E159E2D586" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_101060440EAE04E40FC5F7E159E28F22" xlink:to="loc_aep_ExpectedReimbursementForSpentNuclearFuelDryCaskStorage_EDD8A78C0D42F7491454F7E159E2D586" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/CondensedConsolidatedStatementsOfChangesInEquity" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_A72DFB2F1364BE251BE3F3E4566631BD" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_158F80FA1F813CA9E6CFF3E45666DC34" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_A72DFB2F1364BE251BE3F3E4566631BD" xlink:to="loc_us-gaap_StatementTable_158F80FA1F813CA9E6CFF3E45666DC34" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_040EACE6634A4AB15801F3E4566658B1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_158F80FA1F813CA9E6CFF3E45666DC34" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_040EACE6634A4AB15801F3E4566658B1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_FDB712753437046D7C27F3E4566617E3_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_040EACE6634A4AB15801F3E4566658B1" xlink:to="loc_us-gaap_EquityComponentDomain_FDB712753437046D7C27F3E4566617E3_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_FDB712753437046D7C27F3E4566617E3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_040EACE6634A4AB15801F3E4566658B1" xlink:to="loc_us-gaap_EquityComponentDomain_FDB712753437046D7C27F3E4566617E3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaap_CommonStockMember_8322F352856235EF4A12F3E4566678AF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_FDB712753437046D7C27F3E4566617E3" xlink:to="loc_us-gaap_CommonStockMember_8322F352856235EF4A12F3E4566678AF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_74B3E328FCC9A74E05EFF3E45666BB6B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_FDB712753437046D7C27F3E4566617E3" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_74B3E328FCC9A74E05EFF3E45666BB6B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RetainedEarningsMember" xlink:label="loc_us-gaap_RetainedEarningsMember_04E86258F97E23CE0BE3F3E4566618E0" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_FDB712753437046D7C27F3E4566617E3" xlink:to="loc_us-gaap_RetainedEarningsMember_04E86258F97E23CE0BE3F3E4566618E0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_B13F10BAD62D87176F28F3E456660E61" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_FDB712753437046D7C27F3E4566617E3" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_B13F10BAD62D87176F28F3E456660E61" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NoncontrollingInterestMember" xlink:label="loc_us-gaap_NoncontrollingInterestMember_AC4F1866542278320D6DF3E456663D55" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_FDB712753437046D7C27F3E4566617E3" xlink:to="loc_us-gaap_NoncontrollingInterestMember_AC4F1866542278320D6DF3E456663D55" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_A5240CFD6027C105AA00F3E45666055F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_158F80FA1F813CA9E6CFF3E45666DC34" xlink:to="loc_dei_LegalEntityAxis_A5240CFD6027C105AA00F3E45666055F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_D6E487264DC617D402EFF3E456662963_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_A5240CFD6027C105AA00F3E45666055F" xlink:to="loc_dei_EntityDomain_D6E487264DC617D402EFF3E456662963_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_D6E487264DC617D402EFF3E456662963" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_A5240CFD6027C105AA00F3E45666055F" xlink:to="loc_dei_EntityDomain_D6E487264DC617D402EFF3E456662963" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTransmissionCoMember" xlink:label="loc_aep_AEPTransmissionCoMember_5A48654FBB3B7D5AB583F3E45666DC48" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_D6E487264DC617D402EFF3E456662963" xlink:to="loc_aep_AEPTransmissionCoMember_5A48654FBB3B7D5AB583F3E45666DC48" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTexasInc.Member" xlink:label="loc_aep_AEPTexasInc.Member_DD077B9B90517D9F1DC9F3E456663823" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_D6E487264DC617D402EFF3E456662963" xlink:to="loc_aep_AEPTexasInc.Member_DD077B9B90517D9F1DC9F3E456663823" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AppalachianPowerCoMember" xlink:label="loc_aep_AppalachianPowerCoMember_5DDABB2FE88892FAFE5CF3E456668712" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_D6E487264DC617D402EFF3E456662963" xlink:to="loc_aep_AppalachianPowerCoMember_5DDABB2FE88892FAFE5CF3E456668712" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IndianaMichiganPowerCoMember" xlink:label="loc_aep_IndianaMichiganPowerCoMember_04DBB7EC007B162224A3F3E45666EFF7" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_D6E487264DC617D402EFF3E456662963" xlink:to="loc_aep_IndianaMichiganPowerCoMember_04DBB7EC007B162224A3F3E45666EFF7" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OhioPowerCoMember" xlink:label="loc_aep_OhioPowerCoMember_D52FAB592B6E02F30A53F3E45666E661" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_D6E487264DC617D402EFF3E456662963" xlink:to="loc_aep_OhioPowerCoMember_D52FAB592B6E02F30A53F3E45666E661" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_PublicServiceCoOfOklahomaMember" xlink:label="loc_aep_PublicServiceCoOfOklahomaMember_5294576DF9BA23124931F3E456666B56" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_D6E487264DC617D402EFF3E456662963" xlink:to="loc_aep_PublicServiceCoOfOklahomaMember_5294576DF9BA23124931F3E456666B56" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SouthwesternElectricPowerCoMember" xlink:label="loc_aep_SouthwesternElectricPowerCoMember_979A69CAFE60CB0FDC9AF3E4566637C9" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_D6E487264DC617D402EFF3E456662963" xlink:to="loc_aep_SouthwesternElectricPowerCoMember_979A69CAFE60CB0FDC9AF3E4566637C9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_662E23EAC102623C48FBF3E456660ED1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_A72DFB2F1364BE251BE3F3E4566631BD" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_662E23EAC102623C48FBF3E456660ED1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockSharesIssued" xlink:label="loc_us-gaap_CommonStockSharesIssued_12CF5ECFACB92E8E7E75F3E45666467D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_662E23EAC102623C48FBF3E456660ED1" xlink:to="loc_us-gaap_CommonStockSharesIssued_12CF5ECFACB92E8E7E75F3E45666467D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_973961C3B57BC02FFAC1F3E4566628A9" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_662E23EAC102623C48FBF3E456660ED1" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_973961C3B57BC02FFAC1F3E4566628A9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MembersEquity" xlink:label="loc_us-gaap_MembersEquity_427738ED9E87A53FA0D4F3E45666C253" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_662E23EAC102623C48FBF3E456660ED1" xlink:to="loc_us-gaap_MembersEquity_427738ED9E87A53FA0D4F3E45666C253" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_79AE073FEA2353EB28EDF3E45666DFC1" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_662E23EAC102623C48FBF3E456660ED1" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_79AE073FEA2353EB28EDF3E45666DFC1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_23F24D58EF2F8A5E16ECF3E45666EDDB" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_662E23EAC102623C48FBF3E456660ED1" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_23F24D58EF2F8A5E16ECF3E45666EDDB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DividendsCommonStock" xlink:label="loc_us-gaap_DividendsCommonStock_D720CF3A147C8233CA36F3E4566656CD" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_662E23EAC102623C48FBF3E456660ED1" xlink:to="loc_us-gaap_DividendsCommonStock_D720CF3A147C8233CA36F3E4566656CD" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AffiliatedDividendsCommonStock" xlink:label="loc_aep_AffiliatedDividendsCommonStock_A79DA94DA3AB1F2288B4F3E456665F5C" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_662E23EAC102623C48FBF3E456660ED1" xlink:to="loc_aep_AffiliatedDividendsCommonStock_A79DA94DA3AB1F2288B4F3E456665F5C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders" xlink:label="loc_us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders_15358D627A26EEDE347EF3E4566648B8" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_662E23EAC102623C48FBF3E456660ED1" xlink:to="loc_us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders_15358D627A26EEDE347EF3E4566648B8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockholdersEquityOther" xlink:label="loc_us-gaap_StockholdersEquityOther_0DB03F3EB4D0F6788A2FF3E45666EB33" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_662E23EAC102623C48FBF3E456660ED1" xlink:to="loc_us-gaap_StockholdersEquityOther_0DB03F3EB4D0F6788A2FF3E45666EB33" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromContributionsFromParent" xlink:label="loc_us-gaap_ProceedsFromContributionsFromParent_55275756488CB3F585FFF3E456661CF3" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_662E23EAC102623C48FBF3E456660ED1" xlink:to="loc_us-gaap_ProceedsFromContributionsFromParent_55275756488CB3F585FFF3E456661CF3" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_StockholdersEquityASU201802Adoption" xlink:label="loc_aep_StockholdersEquityASU201802Adoption_920B8112F79C3C33A3E0F3E456660DC6" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_662E23EAC102623C48FBF3E456660ED1" xlink:to="loc_aep_StockholdersEquityASU201802Adoption_920B8112F79C3C33A3E0F3E456660DC6" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_StockholdersEquityASU201601Adoption" xlink:label="loc_aep_StockholdersEquityASU201601Adoption_FB733F08024BA58B4259F3E45666408D" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_662E23EAC102623C48FBF3E456660ED1" xlink:to="loc_aep_StockholdersEquityASU201601Adoption_FB733F08024BA58B4259F3E45666408D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaap_NetIncomeLoss_FC72654B29D55D9BD261F3E45666E77A" xlink:type="locator" />
    <link:definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_662E23EAC102623C48FBF3E456660ED1" xlink:to="loc_us-gaap_NetIncomeLoss_FC72654B29D55D9BD261F3E45666E77A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetIncomeLossAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_7D7D5FAB58495B460E0BF3E45666EF97" xlink:type="locator" />
    <link:definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_662E23EAC102623C48FBF3E456660ED1" xlink:to="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_7D7D5FAB58495B460E0BF3E45666EF97" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProfitLoss" xlink:label="loc_us-gaap_ProfitLoss_559F9BA548B55B986679F3E456665D3B" xlink:type="locator" />
    <link:definitionArc order="15" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_662E23EAC102623C48FBF3E456660ED1" xlink:to="loc_us-gaap_ProfitLoss_559F9BA548B55B986679F3E456665D3B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_45274EA15371B21F6F8AF3E45666589E" xlink:type="locator" />
    <link:definitionArc order="16" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_662E23EAC102623C48FBF3E456660ED1" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_45274EA15371B21F6F8AF3E45666589E" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/ConsolidatedStatementsOfComprehensiveIncomeLoss" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_22519B19AA637DAE030500ECF072019A" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_E1F8FFCA29880396504E00ECF06CD118" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_22519B19AA637DAE030500ECF072019A" xlink:to="loc_us-gaap_StatementTable_E1F8FFCA29880396504E00ECF06CD118" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_4C45E8228137E3CC51C500ECF06C27A0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_E1F8FFCA29880396504E00ECF06CD118" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_4C45E8228137E3CC51C500ECF06C27A0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_B4C0A4B875456C4E7D1300ECF06CC4A9_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_4C45E8228137E3CC51C500ECF06C27A0" xlink:to="loc_us-gaap_EquityComponentDomain_B4C0A4B875456C4E7D1300ECF06CC4A9_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_B4C0A4B875456C4E7D1300ECF06CC4A9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_4C45E8228137E3CC51C500ECF06C27A0" xlink:to="loc_us-gaap_EquityComponentDomain_B4C0A4B875456C4E7D1300ECF06CC4A9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NoncontrollingInterestMember" xlink:label="loc_us-gaap_NoncontrollingInterestMember_309D7CD6BE0F7A3566A600ECF06C22C6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_B4C0A4B875456C4E7D1300ECF06CC4A9" xlink:to="loc_us-gaap_NoncontrollingInterestMember_309D7CD6BE0F7A3566A600ECF06C22C6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_6EF7E4C81204E01E6B5300ECF06D30A6" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_E1F8FFCA29880396504E00ECF06CD118" xlink:to="loc_dei_LegalEntityAxis_6EF7E4C81204E01E6B5300ECF06D30A6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_B197504FFB169F59D9EE00ECF06D3B8B_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_6EF7E4C81204E01E6B5300ECF06D30A6" xlink:to="loc_dei_EntityDomain_B197504FFB169F59D9EE00ECF06D3B8B_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_B197504FFB169F59D9EE00ECF06D3B8B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_6EF7E4C81204E01E6B5300ECF06D30A6" xlink:to="loc_dei_EntityDomain_B197504FFB169F59D9EE00ECF06D3B8B" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTexasInc.Member" xlink:label="loc_aep_AEPTexasInc.Member_079E7F1DF3E3E43195BF00ED5EAC8D5C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_B197504FFB169F59D9EE00ECF06D3B8B" xlink:to="loc_aep_AEPTexasInc.Member_079E7F1DF3E3E43195BF00ED5EAC8D5C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AppalachianPowerCoMember" xlink:label="loc_aep_AppalachianPowerCoMember_220FED74894118B13DDF00ECF06D5871" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_B197504FFB169F59D9EE00ECF06D3B8B" xlink:to="loc_aep_AppalachianPowerCoMember_220FED74894118B13DDF00ECF06D5871" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IndianaMichiganPowerCoMember" xlink:label="loc_aep_IndianaMichiganPowerCoMember_89CDDC24C41F8787E77800ECF06D0603" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_B197504FFB169F59D9EE00ECF06D3B8B" xlink:to="loc_aep_IndianaMichiganPowerCoMember_89CDDC24C41F8787E77800ECF06D0603" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OhioPowerCoMember" xlink:label="loc_aep_OhioPowerCoMember_E8F8BA08794998E5F25300ECF072EEC9" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_B197504FFB169F59D9EE00ECF06D3B8B" xlink:to="loc_aep_OhioPowerCoMember_E8F8BA08794998E5F25300ECF072EEC9" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_PublicServiceCoOfOklahomaMember" xlink:label="loc_aep_PublicServiceCoOfOklahomaMember_90CCB0878302EBA4E7EC00ECF072C15B" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_B197504FFB169F59D9EE00ECF06D3B8B" xlink:to="loc_aep_PublicServiceCoOfOklahomaMember_90CCB0878302EBA4E7EC00ECF072C15B" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SouthwesternElectricPowerCoMember" xlink:label="loc_aep_SouthwesternElectricPowerCoMember_BE8398F0C7DFE4CABED200ECF07205C6" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_B197504FFB169F59D9EE00ECF06D3B8B" xlink:to="loc_aep_SouthwesternElectricPowerCoMember_BE8398F0C7DFE4CABED200ECF07205C6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProfitLoss" xlink:label="loc_us-gaap_ProfitLoss_B37ABDD6B03118ACCD7000ECF072DE91" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_22519B19AA637DAE030500ECF072019A" xlink:to="loc_us-gaap_ProfitLoss_B37ABDD6B03118ACCD7000ECF072DE91" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ComprehensiveIncomeNetOfTaxAbstract" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTaxAbstract_39A6090E9C606901026700ECF072061A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_22519B19AA637DAE030500ECF072019A" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTaxAbstract_39A6090E9C606901026700ECF072061A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesNetOfTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesNetOfTax_18F29B83C374321CF69300ECF073ED74" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTaxAbstract_39A6090E9C606901026700ECF072061A" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesNetOfTax_18F29B83C374321CF69300ECF073ED74" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax_F949E5DEBDA84AEB2CD500ECF073376F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTaxAbstract_39A6090E9C606901026700ECF072061A" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax_F949E5DEBDA84AEB2CD500ECF073376F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_FBB1847F50F7E65763A900ECF073BC8D" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTaxAbstract_39A6090E9C606901026700ECF072061A" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_FBB1847F50F7E65763A900ECF073BC8D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_BD2EBBD9E9535A76FDFF00ECF0738C04" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTaxAbstract_39A6090E9C606901026700ECF072061A" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_BD2EBBD9E9535A76FDFF00ECF0738C04" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_B0FA4B6BA259994ED87C00ECF0736B0D" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_22519B19AA637DAE030500ECF072019A" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_B0FA4B6BA259994ED87C00ECF0736B0D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest_7AD88690F3EAE42349C500ECF0731A0B" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_22519B19AA637DAE030500ECF072019A" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest_7AD88690F3EAE42349C500ECF0731A0B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ComprehensiveIncomeNetOfTax" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTax_30BFF0751F3BBB85D7A500ECF0733B78" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_22519B19AA637DAE030500ECF072019A" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTax_30BFF0751F3BBB85D7A500ECF0733B78" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/ConsolidatedStatementsOfComprehensiveIncomeLossParenthetical" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_7C27809AA422F9176FEFA7557463977A" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_C6EB9A034C29B1F10776A755745CAB2B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_7C27809AA422F9176FEFA7557463977A" xlink:to="loc_us-gaap_StatementTable_C6EB9A034C29B1F10776A755745CAB2B" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_26F14A581F115D24D207A755745C7764" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_C6EB9A034C29B1F10776A755745CAB2B" xlink:to="loc_dei_LegalEntityAxis_26F14A581F115D24D207A755745C7764" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_1AF8068890D158BEEF25A755745DC5C7_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_26F14A581F115D24D207A755745C7764" xlink:to="loc_dei_EntityDomain_1AF8068890D158BEEF25A755745DC5C7_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_1AF8068890D158BEEF25A755745DC5C7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_26F14A581F115D24D207A755745C7764" xlink:to="loc_dei_EntityDomain_1AF8068890D158BEEF25A755745DC5C7" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTexasInc.Member" xlink:label="loc_aep_AEPTexasInc.Member_AF11244ACF1C7028093DA75574620A7B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_1AF8068890D158BEEF25A755745DC5C7" xlink:to="loc_aep_AEPTexasInc.Member_AF11244ACF1C7028093DA75574620A7B" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AppalachianPowerCoMember" xlink:label="loc_aep_AppalachianPowerCoMember_D92CCEFB0CA0AFD3266DA75574629FE1" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_1AF8068890D158BEEF25A755745DC5C7" xlink:to="loc_aep_AppalachianPowerCoMember_D92CCEFB0CA0AFD3266DA75574629FE1" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IndianaMichiganPowerCoMember" xlink:label="loc_aep_IndianaMichiganPowerCoMember_9FCE0B8C055C5C67EAB2A755746259E7" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_1AF8068890D158BEEF25A755745DC5C7" xlink:to="loc_aep_IndianaMichiganPowerCoMember_9FCE0B8C055C5C67EAB2A755746259E7" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OhioPowerCoMember" xlink:label="loc_aep_OhioPowerCoMember_3F816935DA2D4F8509A4A7557463DB76" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_1AF8068890D158BEEF25A755745DC5C7" xlink:to="loc_aep_OhioPowerCoMember_3F816935DA2D4F8509A4A7557463DB76" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_PublicServiceCoOfOklahomaMember" xlink:label="loc_aep_PublicServiceCoOfOklahomaMember_3D7762AF13F0D6F5B232A755746322A2" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_1AF8068890D158BEEF25A755745DC5C7" xlink:to="loc_aep_PublicServiceCoOfOklahomaMember_3D7762AF13F0D6F5B232A755746322A2" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SouthwesternElectricPowerCoMember" xlink:label="loc_aep_SouthwesternElectricPowerCoMember_38EC63539E9B32C31A4FA755746326C1" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_1AF8068890D158BEEF25A755745DC5C7" xlink:to="loc_aep_SouthwesternElectricPowerCoMember_38EC63539E9B32C31A4FA755746326C1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesTax_17E83A814B681E829650A7557463D226" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7C27809AA422F9176FEFA7557463977A" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesTax_17E83A814B681E829650A7557463D226" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesTax_4DEAD18B749C59450600A7557463E703" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7C27809AA422F9176FEFA7557463977A" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesTax_4DEAD18B749C59450600A7557463E703" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax_4CEBBFBA9D16A47A8EE4A7557463FE5E" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7C27809AA422F9176FEFA7557463977A" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax_4CEBBFBA9D16A47A8EE4A7557463FE5E" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/ConsolidatedStatementsOfIncome" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_37478C94E079BE78C76BF80D3D7BA8A0" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_AAE9B95CEAEDD717F334F80D3D7B5B2E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_37478C94E079BE78C76BF80D3D7BA8A0" xlink:to="loc_us-gaap_StatementTable_AAE9B95CEAEDD717F334F80D3D7B5B2E" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_4A60057B5EDBE19B4248F80D3D7BD302" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_AAE9B95CEAEDD717F334F80D3D7B5B2E" xlink:to="loc_dei_LegalEntityAxis_4A60057B5EDBE19B4248F80D3D7BD302" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_219F769DEE5304B2367BF80D3D7BBC79_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_4A60057B5EDBE19B4248F80D3D7BD302" xlink:to="loc_dei_EntityDomain_219F769DEE5304B2367BF80D3D7BBC79_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_219F769DEE5304B2367BF80D3D7BBC79" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_4A60057B5EDBE19B4248F80D3D7BD302" xlink:to="loc_dei_EntityDomain_219F769DEE5304B2367BF80D3D7BBC79" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTexasInc.Member" xlink:label="loc_aep_AEPTexasInc.Member_B97C8D26087C2EBAC9DAF80D3D7B2685" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_219F769DEE5304B2367BF80D3D7BBC79" xlink:to="loc_aep_AEPTexasInc.Member_B97C8D26087C2EBAC9DAF80D3D7B2685" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTransmissionCoMember" xlink:label="loc_aep_AEPTransmissionCoMember_EE8048BF9BD2687A4A68F80D3D7B4D3A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_219F769DEE5304B2367BF80D3D7BBC79" xlink:to="loc_aep_AEPTransmissionCoMember_EE8048BF9BD2687A4A68F80D3D7B4D3A" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AppalachianPowerCoMember" xlink:label="loc_aep_AppalachianPowerCoMember_B168FA725389D8E92360F80D3D7B78DC" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_219F769DEE5304B2367BF80D3D7BBC79" xlink:to="loc_aep_AppalachianPowerCoMember_B168FA725389D8E92360F80D3D7B78DC" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IndianaMichiganPowerCoMember" xlink:label="loc_aep_IndianaMichiganPowerCoMember_F4CF798FF2F31134C87DF80D3D7BE2D2" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_219F769DEE5304B2367BF80D3D7BBC79" xlink:to="loc_aep_IndianaMichiganPowerCoMember_F4CF798FF2F31134C87DF80D3D7BE2D2" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OhioPowerCoMember" xlink:label="loc_aep_OhioPowerCoMember_353357152AD903A05FD1F80D3D7BEF01" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_219F769DEE5304B2367BF80D3D7BBC79" xlink:to="loc_aep_OhioPowerCoMember_353357152AD903A05FD1F80D3D7BEF01" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_PublicServiceCoOfOklahomaMember" xlink:label="loc_aep_PublicServiceCoOfOklahomaMember_7A752D055FCDDAA06E3BF80D3D7BC930" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_219F769DEE5304B2367BF80D3D7BBC79" xlink:to="loc_aep_PublicServiceCoOfOklahomaMember_7A752D055FCDDAA06E3BF80D3D7BC930" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SouthwesternElectricPowerCoMember" xlink:label="loc_aep_SouthwesternElectricPowerCoMember_D2165FD46969F93B5477F80D3D7BD91E" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_219F769DEE5304B2367BF80D3D7BBC79" xlink:to="loc_aep_SouthwesternElectricPowerCoMember_D2165FD46969F93B5477F80D3D7BD91E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RevenuesAbstract" xlink:label="loc_us-gaap_RevenuesAbstract_E1FCE596AD26C7613F1FF80D3D7BE67D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_37478C94E079BE78C76BF80D3D7BA8A0" xlink:to="loc_us-gaap_RevenuesAbstract_E1FCE596AD26C7613F1FF80D3D7BE67D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ElectricUtilityRevenue" xlink:label="loc_us-gaap_ElectricUtilityRevenue_CBFC2CDCE76F051B01A8F80D3D7BFF82" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_E1FCE596AD26C7613F1FF80D3D7BE67D" xlink:to="loc_us-gaap_ElectricUtilityRevenue_CBFC2CDCE76F051B01A8F80D3D7BFF82" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ElectricalTransmissionRevenue" xlink:label="loc_us-gaap_ElectricalTransmissionRevenue_F8E82E6C0F0631650347F80D3D7B31DD" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_E1FCE596AD26C7613F1FF80D3D7BE67D" xlink:to="loc_us-gaap_ElectricalTransmissionRevenue_F8E82E6C0F0631650347F80D3D7B31DD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ElectricalTransmissionAndDistributionRevenue" xlink:label="loc_us-gaap_ElectricalTransmissionAndDistributionRevenue_FB0A6FB8D9B1872BFA0FF80D3D7BE845" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_E1FCE596AD26C7613F1FF80D3D7BE67D" xlink:to="loc_us-gaap_ElectricalTransmissionAndDistributionRevenue_FB0A6FB8D9B1872BFA0FF80D3D7BE845" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ElectricalGenerationRevenue" xlink:label="loc_us-gaap_ElectricalGenerationRevenue_44F5DAB27F2C770A2929F80D3D7BF1F8" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_E1FCE596AD26C7613F1FF80D3D7BE67D" xlink:to="loc_us-gaap_ElectricalGenerationRevenue_44F5DAB27F2C770A2929F80D3D7BF1F8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RevenueFromRelatedParties" xlink:label="loc_us-gaap_RevenueFromRelatedParties_F575914C6924EC451DE6F80D3D7B40ED" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_E1FCE596AD26C7613F1FF80D3D7BE67D" xlink:to="loc_us-gaap_RevenueFromRelatedParties_F575914C6924EC451DE6F80D3D7B40ED" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RelatedPartyTransactionOtherRevenuesFromTransactionsWithRelatedParty" xlink:label="loc_us-gaap_RelatedPartyTransactionOtherRevenuesFromTransactionsWithRelatedParty_0BDEF305427A3DA61521F80D3D7B31C3" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_E1FCE596AD26C7613F1FF80D3D7BE67D" xlink:to="loc_us-gaap_RelatedPartyTransactionOtherRevenuesFromTransactionsWithRelatedParty_0BDEF305427A3DA61521F80D3D7B31C3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherSalesRevenueNet" xlink:label="loc_us-gaap_OtherSalesRevenueNet_7E4DD2C3F90E3F38B025F80D3D7B11F7" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_E1FCE596AD26C7613F1FF80D3D7BE67D" xlink:to="loc_us-gaap_OtherSalesRevenueNet_7E4DD2C3F90E3F38B025F80D3D7B11F7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Revenues" xlink:label="loc_us-gaap_Revenues_A4A8D4A6080E196BDDDEF80D3D7BE738" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_E1FCE596AD26C7613F1FF80D3D7BE67D" xlink:to="loc_us-gaap_Revenues_A4A8D4A6080E196BDDDEF80D3D7BE738" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OperatingExpensesAbstract" xlink:label="loc_us-gaap_OperatingExpensesAbstract_0D9A36DC64EC411CD396F80D3D7B0488" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_37478C94E079BE78C76BF80D3D7BA8A0" xlink:to="loc_us-gaap_OperatingExpensesAbstract_0D9A36DC64EC411CD396F80D3D7B0488" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ElectricProductionExpense" xlink:label="loc_us-gaap_ElectricProductionExpense_772ED3C14C6DC9C6CC6FF80D3D7BBD02" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_0D9A36DC64EC411CD396F80D3D7B0488" xlink:to="loc_us-gaap_ElectricProductionExpense_772ED3C14C6DC9C6CC6FF80D3D7BBD02" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CostOfPurchasedPower" xlink:label="loc_us-gaap_CostOfPurchasedPower_7BC03BB1E614623B8DC7F80D3D7BD0A3" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_0D9A36DC64EC411CD396F80D3D7B0488" xlink:to="loc_us-gaap_CostOfPurchasedPower_7BC03BB1E614623B8DC7F80D3D7BD0A3" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_CostOfPurchasedPowerFromAffiliate" xlink:label="loc_aep_CostOfPurchasedPowerFromAffiliate_1625D3BD7F757F39CFE2F80D3D7B8A81" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_0D9A36DC64EC411CD396F80D3D7B0488" xlink:to="loc_aep_CostOfPurchasedPowerFromAffiliate_1625D3BD7F757F39CFE2F80D3D7B8A81" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AmortizationOfGenerationDeferrals" xlink:label="loc_aep_AmortizationOfGenerationDeferrals_C3C24FA2CADE3DD3027FF80D3D7B57E4" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_0D9A36DC64EC411CD396F80D3D7B0488" xlink:to="loc_aep_AmortizationOfGenerationDeferrals_C3C24FA2CADE3DD3027FF80D3D7B57E4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_UtilitiesOperatingExpenseOperations" xlink:label="loc_us-gaap_UtilitiesOperatingExpenseOperations_30814FC083E13D1A1580F80D3D7B235D" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_0D9A36DC64EC411CD396F80D3D7B0488" xlink:to="loc_us-gaap_UtilitiesOperatingExpenseOperations_30814FC083E13D1A1580F80D3D7B235D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_UtilitiesOperatingExpenseMaintenance" xlink:label="loc_us-gaap_UtilitiesOperatingExpenseMaintenance_028E3C38281E4FD7E9BBF80D3D7BE8A5" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_0D9A36DC64EC411CD396F80D3D7B0488" xlink:to="loc_us-gaap_UtilitiesOperatingExpenseMaintenance_028E3C38281E4FD7E9BBF80D3D7BE8A5" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_GainonSaleofMerchantGenerationAssets" xlink:label="loc_aep_GainonSaleofMerchantGenerationAssets_C74BCC04407BB93A2F73F80D3D7BCF5B" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_0D9A36DC64EC411CD396F80D3D7B0488" xlink:to="loc_aep_GainonSaleofMerchantGenerationAssets_C74BCC04407BB93A2F73F80D3D7BCF5B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_UtilitiesOperatingExpenseDepreciationAndAmortization" xlink:label="loc_us-gaap_UtilitiesOperatingExpenseDepreciationAndAmortization_E8D9522D8A65D8397DC9F80D3D7BD9E0" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_0D9A36DC64EC411CD396F80D3D7B0488" xlink:to="loc_us-gaap_UtilitiesOperatingExpenseDepreciationAndAmortization_E8D9522D8A65D8397DC9F80D3D7BD9E0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TaxesExcludingIncomeAndExciseTaxes" xlink:label="loc_us-gaap_TaxesExcludingIncomeAndExciseTaxes_DE85B314D8B4EF4A99B5F80D3D7B882E" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_0D9A36DC64EC411CD396F80D3D7B0488" xlink:to="loc_us-gaap_TaxesExcludingIncomeAndExciseTaxes_DE85B314D8B4EF4A99B5F80D3D7B882E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OperatingExpenses" xlink:label="loc_us-gaap_OperatingExpenses_B14C1B6479348FB6FEF5F80D3D7BA2A9" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_0D9A36DC64EC411CD396F80D3D7B0488" xlink:to="loc_us-gaap_OperatingExpenses_B14C1B6479348FB6FEF5F80D3D7BA2A9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OperatingIncomeLoss" xlink:label="loc_us-gaap_OperatingIncomeLoss_770C413CDEB7F5219771F80D3D7B005B" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_37478C94E079BE78C76BF80D3D7BA8A0" xlink:to="loc_us-gaap_OperatingIncomeLoss_770C413CDEB7F5219771F80D3D7B005B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherNonoperatingIncomeExpenseAbstract" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_732B8D2D995376AF3DD8F80D3D7B7C34" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_37478C94E079BE78C76BF80D3D7BA8A0" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_732B8D2D995376AF3DD8F80D3D7B7C34" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentIncomeNet" xlink:label="loc_us-gaap_InvestmentIncomeNet_D834FBDF547B31B57CE3F80D3D7B76AD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_732B8D2D995376AF3DD8F80D3D7B7C34" xlink:to="loc_us-gaap_InvestmentIncomeNet_D834FBDF547B31B57CE3F80D3D7B76AD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentIncomeInterestAndDividend" xlink:label="loc_us-gaap_InvestmentIncomeInterestAndDividend_BDE2529D3107884EC385F80D3D7BC2B1" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_732B8D2D995376AF3DD8F80D3D7B7C34" xlink:to="loc_us-gaap_InvestmentIncomeInterestAndDividend_BDE2529D3107884EC385F80D3D7BC2B1" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_CarryingCostsIncome" xlink:label="loc_aep_CarryingCostsIncome_44DD1C5472F238196380F80D3D7B4252" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_732B8D2D995376AF3DD8F80D3D7B7C34" xlink:to="loc_aep_CarryingCostsIncome_44DD1C5472F238196380F80D3D7B4252" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity" xlink:label="loc_us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity_7160F3FBBC7BA7469015F80D3D7B3109" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_732B8D2D995376AF3DD8F80D3D7B7C34" xlink:to="loc_us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity_7160F3FBBC7BA7469015F80D3D7B3109" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherNonoperatingIncomeExpense" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_5E041BAB29C29FBB2DDBF80D3D7B94F1" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_732B8D2D995376AF3DD8F80D3D7B7C34" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_5E041BAB29C29FBB2DDBF80D3D7B94F1" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_NonServiceCostComponentsofNetPeriodicBenefitCost" xlink:label="loc_aep_NonServiceCostComponentsofNetPeriodicBenefitCost_E936E6760670492E401AF80D3D7B5A58" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_732B8D2D995376AF3DD8F80D3D7B7C34" xlink:to="loc_aep_NonServiceCostComponentsofNetPeriodicBenefitCost_E936E6760670492E401AF80D3D7B5A58" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InterestExpense" xlink:label="loc_us-gaap_InterestExpense_28C93198A166D000D1BAF80D3D7B3C0A" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_732B8D2D995376AF3DD8F80D3D7B7C34" xlink:to="loc_us-gaap_InterestExpense_28C93198A166D000D1BAF80D3D7B3C0A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_62BFE7E98128D8CABE1AF80D3D7B45A9" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_37478C94E079BE78C76BF80D3D7BA8A0" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_62BFE7E98128D8CABE1AF80D3D7B45A9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_09E8F62749D45BD01D67F80D3D7BD6A4" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_37478C94E079BE78C76BF80D3D7BA8A0" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_09E8F62749D45BD01D67F80D3D7BD6A4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeLossFromEquityMethodInvestments" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_3E82C02B94151BECB29CF80D3D7B81D0" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_37478C94E079BE78C76BF80D3D7BA8A0" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_3E82C02B94151BECB29CF80D3D7B81D0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProfitLoss" xlink:label="loc_us-gaap_ProfitLoss_6C3A85B37CEB02BACE0CF80D3D7B151C" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_37478C94E079BE78C76BF80D3D7BA8A0" xlink:to="loc_us-gaap_ProfitLoss_6C3A85B37CEB02BACE0CF80D3D7B151C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetIncomeLossAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_D63AE4EDB0C6AADCF4CBF80D3D7BF5DB" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_37478C94E079BE78C76BF80D3D7BA8A0" xlink:to="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_D63AE4EDB0C6AADCF4CBF80D3D7BF5DB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_A75BB664FA4EFD28A674F80D3D7B12F0" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_37478C94E079BE78C76BF80D3D7BA8A0" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_A75BB664FA4EFD28A674F80D3D7B12F0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EarningsPerShareAbstract" xlink:label="loc_us-gaap_EarningsPerShareAbstract_B954B8F9EF70E089AAC9F80D3D7BDAB5" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_37478C94E079BE78C76BF80D3D7BA8A0" xlink:to="loc_us-gaap_EarningsPerShareAbstract_B954B8F9EF70E089AAC9F80D3D7BDAB5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_B08D69C3CE09F6B4EFA6F80D3D7B22D4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_B954B8F9EF70E089AAC9F80D3D7BDAB5" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_B08D69C3CE09F6B4EFA6F80D3D7B22D4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EarningsPerShareBasic" xlink:label="loc_us-gaap_EarningsPerShareBasic_10163DDE50433CF2D101F80D3D7B9DCB" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_B954B8F9EF70E089AAC9F80D3D7BDAB5" xlink:to="loc_us-gaap_EarningsPerShareBasic_10163DDE50433CF2D101F80D3D7B9DCB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_0981C1519BEF4ADBCACFF80D3D7B8E92" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_B954B8F9EF70E089AAC9F80D3D7BDAB5" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_0981C1519BEF4ADBCACFF80D3D7B8E92" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EarningsPerShareDiluted" xlink:label="loc_us-gaap_EarningsPerShareDiluted_37693502693C0EC10E6BF80D3D7B595B" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_B954B8F9EF70E089AAC9F80D3D7BDAB5" xlink:to="loc_us-gaap_EarningsPerShareDiluted_37693502693C0EC10E6BF80D3D7B595B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockDividendsPerShareDeclared" xlink:label="loc_us-gaap_CommonStockDividendsPerShareDeclared_F8E0D0D512B3C18C7716F80D3D7B7B2D" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_B954B8F9EF70E089AAC9F80D3D7BDAB5" xlink:to="loc_us-gaap_CommonStockDividendsPerShareDeclared_F8E0D0D512B3C18C7716F80D3D7B7B2D" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/DerivativesAndHedging" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_67A0AA07DDE8BDBC8E568751A77B9F0D" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_3F9A8AAD857A4C926F388751A77BDAE6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_67A0AA07DDE8BDBC8E568751A77B9F0D" xlink:to="loc_us-gaap_StatementTable_3F9A8AAD857A4C926F388751A77BDAE6" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_4FAA07D75651267F903C8751A77B156E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_3F9A8AAD857A4C926F388751A77BDAE6" xlink:to="loc_dei_LegalEntityAxis_4FAA07D75651267F903C8751A77B156E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_651CB3026E7790E3545F8751A77BE2B3_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_4FAA07D75651267F903C8751A77B156E" xlink:to="loc_dei_EntityDomain_651CB3026E7790E3545F8751A77BE2B3_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_651CB3026E7790E3545F8751A77BE2B3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_4FAA07D75651267F903C8751A77B156E" xlink:to="loc_dei_EntityDomain_651CB3026E7790E3545F8751A77BE2B3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureTextBlock" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureTextBlock_CB1733B4C1AE15A634E88751A77BF244" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_67A0AA07DDE8BDBC8E568751A77B9F0D" xlink:to="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureTextBlock_CB1733B4C1AE15A634E88751A77BF244" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/DerivativesAndHedgingDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_2A2AE0840F203DCAA273F8A4D0AE9EBA" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_AB9477015426E6B01171F8A4D0A329B7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_2A2AE0840F203DCAA273F8A4D0AE9EBA" xlink:to="loc_us-gaap_StatementTable_AB9477015426E6B01171F8A4D0A329B7" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_90AF779320F042ACFB53F8A4D0A3366C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_AB9477015426E6B01171F8A4D0A329B7" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_90AF779320F042ACFB53F8A4D0A3366C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_6D19E9CE692753A115E8F8A4D0A4E048_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_90AF779320F042ACFB53F8A4D0A3366C" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_6D19E9CE692753A115E8F8A4D0A4E048_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_6D19E9CE692753A115E8F8A4D0A4E048" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_90AF779320F042ACFB53F8A4D0A3366C" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_6D19E9CE692753A115E8F8A4D0A4E048" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_VerticallyIntegratedUtilitiesRevenuesMember" xlink:label="loc_aep_VerticallyIntegratedUtilitiesRevenuesMember_F2B461B028C3F529A0BEF8A4D0A4F219" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_6D19E9CE692753A115E8F8A4D0A4E048" xlink:to="loc_aep_VerticallyIntegratedUtilitiesRevenuesMember_F2B461B028C3F529A0BEF8A4D0A4F219" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_GenerationAndMarketingRevenuesMember" xlink:label="loc_aep_GenerationAndMarketingRevenuesMember_D9233BC2C41DF8BF34E7F8A4D0A4A720" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_6D19E9CE692753A115E8F8A4D0A4E048" xlink:to="loc_aep_GenerationAndMarketingRevenuesMember_D9233BC2C41DF8BF34E7F8A4D0A4A720" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ElectricGenerationTransmissionDistributionRevenuesMember" xlink:label="loc_aep_ElectricGenerationTransmissionDistributionRevenuesMember_94133563098838B03BC4F8A4D0A400D1" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_6D19E9CE692753A115E8F8A4D0A4E048" xlink:to="loc_aep_ElectricGenerationTransmissionDistributionRevenuesMember_94133563098838B03BC4F8A4D0A400D1" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_PurchasedElectricityForResaleMember" xlink:label="loc_aep_PurchasedElectricityForResaleMember_F9FE37F936865A40881EF8A4D0A4E9A1" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_6D19E9CE692753A115E8F8A4D0A4E048" xlink:to="loc_aep_PurchasedElectricityForResaleMember_F9FE37F936865A40881EF8A4D0A4E9A1" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OtherOperationExpenseMember" xlink:label="loc_aep_OtherOperationExpenseMember_E203E2B25A784CAE5A61F8A4D0A4FB83" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_6D19E9CE692753A115E8F8A4D0A4E048" xlink:to="loc_aep_OtherOperationExpenseMember_E203E2B25A784CAE5A61F8A4D0A4FB83" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaintenanceExpenseMember" xlink:label="loc_aep_MaintenanceExpenseMember_CBD742B49FBC234ECB8EF8A4D0A406BC" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_6D19E9CE692753A115E8F8A4D0A4E048" xlink:to="loc_aep_MaintenanceExpenseMember_CBD742B49FBC234ECB8EF8A4D0A406BC" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RegulatoryAssetsMember" xlink:label="loc_aep_RegulatoryAssetsMember_A51A3D600D3FCD1D84BEF8A4D0A4F6F0" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_6D19E9CE692753A115E8F8A4D0A4E048" xlink:to="loc_aep_RegulatoryAssetsMember_A51A3D600D3FCD1D84BEF8A4D0A4F6F0" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RegulatoryLiabilitiesMember" xlink:label="loc_aep_RegulatoryLiabilitiesMember_B7AFFCE8DE1E623AFE46F8A4D0A5E90F" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_6D19E9CE692753A115E8F8A4D0A4E048" xlink:to="loc_aep_RegulatoryLiabilitiesMember_B7AFFCE8DE1E623AFE46F8A4D0A5E90F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_5700337D52244AD30944F8A4D0A53AF4" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_AB9477015426E6B01171F8A4D0A329B7" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_5700337D52244AD30944F8A4D0A53AF4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_F7D7B15018E07FC14434F8A4D0A5FF1D_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_5700337D52244AD30944F8A4D0A53AF4" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_F7D7B15018E07FC14434F8A4D0A5FF1D_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_F7D7B15018E07FC14434F8A4D0A5FF1D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_5700337D52244AD30944F8A4D0A53AF4" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_F7D7B15018E07FC14434F8A4D0A5FF1D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommodityContractMember" xlink:label="loc_us-gaap_CommodityContractMember_7289B3A16F27DEA02557F8A4D0A56658" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_F7D7B15018E07FC14434F8A4D0A5FF1D" xlink:to="loc_us-gaap_CommodityContractMember_7289B3A16F27DEA02557F8A4D0A56658" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_InterestRateMember" xlink:label="loc_aep_InterestRateMember_4642F01EF131AFAD71D2F8A4D0A53215" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_F7D7B15018E07FC14434F8A4D0A5FF1D" xlink:to="loc_aep_InterestRateMember_4642F01EF131AFAD71D2F8A4D0A53215" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_GrossAmountsOfRiskManagementAssetsLiabilitiesRecognizedMember" xlink:label="loc_aep_GrossAmountsOfRiskManagementAssetsLiabilitiesRecognizedMember_9D674ECE066AE2871A06F8A4D0A549AD" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_F7D7B15018E07FC14434F8A4D0A5FF1D" xlink:to="loc_aep_GrossAmountsOfRiskManagementAssetsLiabilitiesRecognizedMember_9D674ECE066AE2871A06F8A4D0A549AD" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_GrossAmountsOffsetInStatementOfFinancialPositionMember" xlink:label="loc_aep_GrossAmountsOffsetInStatementOfFinancialPositionMember_64C763F61D18EAC54BB1F8A4D0A51848" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_F7D7B15018E07FC14434F8A4D0A5FF1D" xlink:to="loc_aep_GrossAmountsOffsetInStatementOfFinancialPositionMember_64C763F61D18EAC54BB1F8A4D0A51848" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_NetAmountsOfAssetsLiabilitiesPresentedInStatementOfFinancialPositionMember" xlink:label="loc_aep_NetAmountsOfAssetsLiabilitiesPresentedInStatementOfFinancialPositionMember_8D6802B17E3F860E94A8F8A4D0A5EE62" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_F7D7B15018E07FC14434F8A4D0A5FF1D" xlink:to="loc_aep_NetAmountsOfAssetsLiabilitiesPresentedInStatementOfFinancialPositionMember_8D6802B17E3F860E94A8F8A4D0A5EE62" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_PowerContractMember" xlink:label="loc_aep_PowerContractMember_36E02B54453F440F5CC4F8A4D0AA03C6" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_F7D7B15018E07FC14434F8A4D0A5FF1D" xlink:to="loc_aep_PowerContractMember_36E02B54453F440F5CC4F8A4D0AA03C6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CoalContractMember" xlink:label="loc_us-gaap_CoalContractMember_DB795E834A2222991EB7F8A4D0AB0061" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_F7D7B15018E07FC14434F8A4D0A5FF1D" xlink:to="loc_us-gaap_CoalContractMember_DB795E834A2222991EB7F8A4D0AB0061" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_NaturalGasContractMember" xlink:label="loc_aep_NaturalGasContractMember_9F033CB1BA7366F7FB40F8A4D0ABF077" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_F7D7B15018E07FC14434F8A4D0A5FF1D" xlink:to="loc_aep_NaturalGasContractMember_9F033CB1BA7366F7FB40F8A4D0ABF077" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_HeatingOilAndGasolineContractMember" xlink:label="loc_aep_HeatingOilAndGasolineContractMember_79B5F7520D8DFCEA3AC5F8A4D0ACBD32" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_F7D7B15018E07FC14434F8A4D0A5FF1D" xlink:to="loc_aep_HeatingOilAndGasolineContractMember_79B5F7520D8DFCEA3AC5F8A4D0ACBD32" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InterestRateContractMember" xlink:label="loc_us-gaap_InterestRateContractMember_9FB0EC6DA593FCE8AAECF8A4D0AC0130" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_F7D7B15018E07FC14434F8A4D0A5FF1D" xlink:to="loc_us-gaap_InterestRateContractMember_9FB0EC6DA593FCE8AAECF8A4D0AC0130" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_F675065C1EDDD481B448F8A4D0ACEFE1" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_AB9477015426E6B01171F8A4D0A329B7" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_F675065C1EDDD481B448F8A4D0ACEFE1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_HedgingRelationshipDomain" xlink:label="loc_us-gaap_HedgingRelationshipDomain_B66E6C3D40EB0C62D9A1F8A4D0AC6B47_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_F675065C1EDDD481B448F8A4D0ACEFE1" xlink:to="loc_us-gaap_HedgingRelationshipDomain_B66E6C3D40EB0C62D9A1F8A4D0AC6B47_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_HedgingRelationshipDomain" xlink:label="loc_us-gaap_HedgingRelationshipDomain_B66E6C3D40EB0C62D9A1F8A4D0AC6B47" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_F675065C1EDDD481B448F8A4D0ACEFE1" xlink:to="loc_us-gaap_HedgingRelationshipDomain_B66E6C3D40EB0C62D9A1F8A4D0AC6B47" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RiskManagementCommodityContractsMember" xlink:label="loc_aep_RiskManagementCommodityContractsMember_2B816DE967BF820574F9F8A4D0ACAC6E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_B66E6C3D40EB0C62D9A1F8A4D0AC6B47" xlink:to="loc_aep_RiskManagementCommodityContractsMember_2B816DE967BF820574F9F8A4D0ACAC6E" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_HedgingContractsMember" xlink:label="loc_aep_HedgingContractsMember_F226FACBDA436127EE48F8A4D0AC7B44" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_B66E6C3D40EB0C62D9A1F8A4D0AC6B47" xlink:to="loc_aep_HedgingContractsMember_F226FACBDA436127EE48F8A4D0AC7B44" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_8A4124592025FB13130FF8A4D0ACBD56" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_AB9477015426E6B01171F8A4D0A329B7" xlink:to="loc_dei_LegalEntityAxis_8A4124592025FB13130FF8A4D0ACBD56" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_5CBD12E862BC3C2B855BF8A4D0AC546A_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_8A4124592025FB13130FF8A4D0ACBD56" xlink:to="loc_dei_EntityDomain_5CBD12E862BC3C2B855BF8A4D0AC546A_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_5CBD12E862BC3C2B855BF8A4D0AC546A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_8A4124592025FB13130FF8A4D0ACBD56" xlink:to="loc_dei_EntityDomain_5CBD12E862BC3C2B855BF8A4D0AC546A" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTexasInc.Member" xlink:label="loc_aep_AEPTexasInc.Member_E91A63D26AA04CF6471CF8A4D0ACA2BB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_5CBD12E862BC3C2B855BF8A4D0AC546A" xlink:to="loc_aep_AEPTexasInc.Member_E91A63D26AA04CF6471CF8A4D0ACA2BB" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AppalachianPowerCoMember" xlink:label="loc_aep_AppalachianPowerCoMember_8B69BCD1207B7329FA9EF8A4D0AC2684" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_5CBD12E862BC3C2B855BF8A4D0AC546A" xlink:to="loc_aep_AppalachianPowerCoMember_8B69BCD1207B7329FA9EF8A4D0AC2684" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IndianaMichiganPowerCoMember" xlink:label="loc_aep_IndianaMichiganPowerCoMember_969A8D24157E0548604AF8A4D0AC57C4" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_5CBD12E862BC3C2B855BF8A4D0AC546A" xlink:to="loc_aep_IndianaMichiganPowerCoMember_969A8D24157E0548604AF8A4D0AC57C4" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OhioPowerCoMember" xlink:label="loc_aep_OhioPowerCoMember_AF7AF44BD5EA00D1301DF8A4D0AEF439" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_5CBD12E862BC3C2B855BF8A4D0AC546A" xlink:to="loc_aep_OhioPowerCoMember_AF7AF44BD5EA00D1301DF8A4D0AEF439" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_PublicServiceCoOfOklahomaMember" xlink:label="loc_aep_PublicServiceCoOfOklahomaMember_32B9224A985004EA1A6AF8A4D0AE09B6" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_5CBD12E862BC3C2B855BF8A4D0AC546A" xlink:to="loc_aep_PublicServiceCoOfOklahomaMember_32B9224A985004EA1A6AF8A4D0AE09B6" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SouthwesternElectricPowerCoMember" xlink:label="loc_aep_SouthwesternElectricPowerCoMember_23352D8EAE03D6AAA3EAF8A4D0AE6F1D" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_5CBD12E862BC3C2B855BF8A4D0AC546A" xlink:to="loc_aep_SouthwesternElectricPowerCoMember_23352D8EAE03D6AAA3EAF8A4D0AE6F1D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeGainLossOnDerivativeNet" xlink:label="loc_us-gaap_DerivativeGainLossOnDerivativeNet_C6BB16B880B8B2834262F8A4D0AED8ED" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_2A2AE0840F203DCAA273F8A4D0AE9EBA" xlink:to="loc_us-gaap_DerivativeGainLossOnDerivativeNet_C6BB16B880B8B2834262F8A4D0AED8ED" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_GainLossOnFairValuePortionOfLongTermDebt" xlink:label="loc_aep_GainLossOnFairValuePortionOfLongTermDebt_DA1B58002A3EB46EC09AF8A4D0B85BEE" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_2A2AE0840F203DCAA273F8A4D0AE9EBA" xlink:to="loc_aep_GainLossOnFairValuePortionOfLongTermDebt_DA1B58002A3EB46EC09AF8A4D0B85BEE" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_NotionalVolumeOfDerivativeInstrumentsAbstract" xlink:label="loc_aep_NotionalVolumeOfDerivativeInstrumentsAbstract_D6B584CD1B2A429B00D6F8A4D0AE49EA" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_2A2AE0840F203DCAA273F8A4D0AE9EBA" xlink:to="loc_aep_NotionalVolumeOfDerivativeInstrumentsAbstract_D6B584CD1B2A429B00D6F8A4D0AE49EA" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_CommodityAbstract" xlink:label="loc_aep_CommodityAbstract_06E2A8A9A13FB9FE0D91F8A4D0AEEA00" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_NotionalVolumeOfDerivativeInstrumentsAbstract_D6B584CD1B2A429B00D6F8A4D0AE49EA" xlink:to="loc_aep_CommodityAbstract_06E2A8A9A13FB9FE0D91F8A4D0AEEA00" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_DerivativeNonmonetaryEnergyNotionalAmount" xlink:label="loc_aep_DerivativeNonmonetaryEnergyNotionalAmount_A386B370C19875807490F8A4D0AEFFAB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CommodityAbstract_06E2A8A9A13FB9FE0D91F8A4D0AEEA00" xlink:to="loc_aep_DerivativeNonmonetaryEnergyNotionalAmount_A386B370C19875807490F8A4D0AEFFAB" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_DerivativeNonmonetaryMassNotionalAmount" xlink:label="loc_aep_DerivativeNonmonetaryMassNotionalAmount_55F47937C8F1D498BBC0F8A4D0AE5AA2" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CommodityAbstract_06E2A8A9A13FB9FE0D91F8A4D0AEEA00" xlink:to="loc_aep_DerivativeNonmonetaryMassNotionalAmount_55F47937C8F1D498BBC0F8A4D0AE5AA2" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_DerivativeNonmonetaryVolumeNotionalAmount" xlink:label="loc_aep_DerivativeNonmonetaryVolumeNotionalAmount_D8F56142BF6740D18652F8A4D0AEBB68" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CommodityAbstract_06E2A8A9A13FB9FE0D91F8A4D0AEEA00" xlink:to="loc_aep_DerivativeNonmonetaryVolumeNotionalAmount_D8F56142BF6740D18652F8A4D0AEBB68" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/invest/2013/invest-2013-01-31.xsd#invest_DerivativeNotionalAmount" xlink:label="loc_invest_DerivativeNotionalAmount_57A65CD58D26848D1EE3F8A4D0AEB866" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CommodityAbstract_06E2A8A9A13FB9FE0D91F8A4D0AEEA00" xlink:to="loc_invest_DerivativeNotionalAmount_57A65CD58D26848D1EE3F8A4D0AEB866" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_CashCollateralNettingAbstract" xlink:label="loc_aep_CashCollateralNettingAbstract_2DD14FC9A319D60B1CA5F8A4D0AECD53" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_2A2AE0840F203DCAA273F8A4D0AE9EBA" xlink:to="loc_aep_CashCollateralNettingAbstract_2DD14FC9A319D60B1CA5F8A4D0AECD53" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SecuritiesReceivedAsCollateral" xlink:label="loc_us-gaap_SecuritiesReceivedAsCollateral_D291029C45D723F1301CF8A4D0AF9A70" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CashCollateralNettingAbstract_2DD14FC9A319D60B1CA5F8A4D0AECD53" xlink:to="loc_us-gaap_SecuritiesReceivedAsCollateral_D291029C45D723F1301CF8A4D0AF9A70" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ObligationToReturnSecuritiesReceivedAsCollateral" xlink:label="loc_us-gaap_ObligationToReturnSecuritiesReceivedAsCollateral_E2FF68ED0FF2A54E4913F8A4D0AF721C" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CashCollateralNettingAbstract_2DD14FC9A319D60B1CA5F8A4D0AECD53" xlink:to="loc_us-gaap_ObligationToReturnSecuritiesReceivedAsCollateral_E2FF68ED0FF2A54E4913F8A4D0AF721C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeInstrumentDetailAbstract" xlink:label="loc_us-gaap_DerivativeInstrumentDetailAbstract_7767F2E568826C18AA3AF8A4D0AFCFA9" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_2A2AE0840F203DCAA273F8A4D0AE9EBA" xlink:to="loc_us-gaap_DerivativeInstrumentDetailAbstract_7767F2E568826C18AA3AF8A4D0AFCFA9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeAssetsCurrent" xlink:label="loc_us-gaap_DerivativeAssetsCurrent_636C3A9422844ACC10F2F8A4D0B0E818" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentDetailAbstract_7767F2E568826C18AA3AF8A4D0AFCFA9" xlink:to="loc_us-gaap_DerivativeAssetsCurrent_636C3A9422844ACC10F2F8A4D0B0E818" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeAssetsNoncurrent" xlink:label="loc_us-gaap_DerivativeAssetsNoncurrent_B7441A956014ACF0F026F8A4D0B08B86" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentDetailAbstract_7767F2E568826C18AA3AF8A4D0AFCFA9" xlink:to="loc_us-gaap_DerivativeAssetsNoncurrent_B7441A956014ACF0F026F8A4D0B08B86" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeAssets" xlink:label="loc_us-gaap_DerivativeAssets_7A5646A790E7EBF31910F8A4D0B00276" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentDetailAbstract_7767F2E568826C18AA3AF8A4D0AFCFA9" xlink:to="loc_us-gaap_DerivativeAssets_7A5646A790E7EBF31910F8A4D0B00276" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeLiabilitiesCurrent" xlink:label="loc_us-gaap_DerivativeLiabilitiesCurrent_83C277FA9D099A44B665F8A4D0B06A3D" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentDetailAbstract_7767F2E568826C18AA3AF8A4D0AFCFA9" xlink:to="loc_us-gaap_DerivativeLiabilitiesCurrent_83C277FA9D099A44B665F8A4D0B06A3D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeLiabilitiesNoncurrent" xlink:label="loc_us-gaap_DerivativeLiabilitiesNoncurrent_76C2B2620034B5A36ABFF8A4D0B02FB1" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentDetailAbstract_7767F2E568826C18AA3AF8A4D0AFCFA9" xlink:to="loc_us-gaap_DerivativeLiabilitiesNoncurrent_76C2B2620034B5A36ABFF8A4D0B02FB1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeLiabilities" xlink:label="loc_us-gaap_DerivativeLiabilities_DBC2511F9F7ADD01BD34F8A4D0B045F5" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentDetailAbstract_7767F2E568826C18AA3AF8A4D0AFCFA9" xlink:to="loc_us-gaap_DerivativeLiabilities_DBC2511F9F7ADD01BD34F8A4D0B045F5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet" xlink:label="loc_us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet_CB0CBFB4653D64AE4705F8A4D0B1C4C8" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentDetailAbstract_7767F2E568826C18AA3AF8A4D0AFCFA9" xlink:to="loc_us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet_CB0CBFB4653D64AE4705F8A4D0B1C4C8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GainLossOnDerivativeInstrumentsNetPretaxAbstract" xlink:label="loc_us-gaap_GainLossOnDerivativeInstrumentsNetPretaxAbstract_0904DB227AFDE00F5DE7F8A4D0B13324" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_2A2AE0840F203DCAA273F8A4D0AE9EBA" xlink:to="loc_us-gaap_GainLossOnDerivativeInstrumentsNetPretaxAbstract_0904DB227AFDE00F5DE7F8A4D0B13324" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GainLossOnDerivativeInstrumentsNetPretax" xlink:label="loc_us-gaap_GainLossOnDerivativeInstrumentsNetPretax_802848C8B00DF40F0E55F8A4D0B6095F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GainLossOnDerivativeInstrumentsNetPretaxAbstract_0904DB227AFDE00F5DE7F8A4D0B13324" xlink:to="loc_us-gaap_GainLossOnDerivativeInstrumentsNetPretax_802848C8B00DF40F0E55F8A4D0B6095F" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_DerivativeRiskManagementContractsGainLossRecognizedAsRegulatoryAssetLiability" xlink:label="loc_aep_DerivativeRiskManagementContractsGainLossRecognizedAsRegulatoryAssetLiability_49E8F54BE372345140A0F8A4D0B66EE1" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GainLossOnDerivativeInstrumentsNetPretaxAbstract_0904DB227AFDE00F5DE7F8A4D0B13324" xlink:to="loc_aep_DerivativeRiskManagementContractsGainLossRecognizedAsRegulatoryAssetLiability_49E8F54BE372345140A0F8A4D0B66EE1" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ImpactOfCashFlowHedgesOnBalanceSheetAbstract" xlink:label="loc_aep_ImpactOfCashFlowHedgesOnBalanceSheetAbstract_96225E83E82B51A4825BF8A4D0B6D000" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_2A2AE0840F203DCAA273F8A4D0AE9EBA" xlink:to="loc_aep_ImpactOfCashFlowHedgesOnBalanceSheetAbstract_96225E83E82B51A4825BF8A4D0B6D000" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_HedgingAssets" xlink:label="loc_aep_HedgingAssets_7F427C7A86460B311EB0F8A4D0B6809D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_ImpactOfCashFlowHedgesOnBalanceSheetAbstract_96225E83E82B51A4825BF8A4D0B6D000" xlink:to="loc_aep_HedgingAssets_7F427C7A86460B311EB0F8A4D0B6809D" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_HedgingLiabilities" xlink:label="loc_aep_HedgingLiabilities_89670FBBCB3192159E69F8A4D0B7A527" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_ImpactOfCashFlowHedgesOnBalanceSheetAbstract_96225E83E82B51A4825BF8A4D0B6D000" xlink:to="loc_aep_HedgingLiabilities_89670FBBCB3192159E69F8A4D0B7A527" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossCumulativeChangesInNetGainLossFromCashFlowHedgesEffectNetOfTax" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossCumulativeChangesInNetGainLossFromCashFlowHedgesEffectNetOfTax_FD81F65C8C093E32B4D2F8A4D0B75E7D" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_ImpactOfCashFlowHedgesOnBalanceSheetAbstract_96225E83E82B51A4825BF8A4D0B6D000" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossCumulativeChangesInNetGainLossFromCashFlowHedgesEffectNetOfTax_FD81F65C8C093E32B4D2F8A4D0B75E7D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths" xlink:label="loc_us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths_970537345DC56BC4CF7DF8A4D0B77D04" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_ImpactOfCashFlowHedgesOnBalanceSheetAbstract_96225E83E82B51A4825BF8A4D0B6D000" xlink:to="loc_us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths_970537345DC56BC4CF7DF8A4D0B77D04" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_CollateralTriggeringEventsAbstract" xlink:label="loc_aep_CollateralTriggeringEventsAbstract_6B866E4F9737DE7B5A26F8A4D0B76081" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_2A2AE0840F203DCAA273F8A4D0AE9EBA" xlink:to="loc_aep_CollateralTriggeringEventsAbstract_6B866E4F9737DE7B5A26F8A4D0B76081" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_FairValueOfDerivativeLiabilitiesSubjectToCrossDefaultProvisions" xlink:label="loc_aep_FairValueOfDerivativeLiabilitiesSubjectToCrossDefaultProvisions_01289F0892913747E235F8A4D0B73239" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CollateralTriggeringEventsAbstract_6B866E4F9737DE7B5A26F8A4D0B76081" xlink:to="loc_aep_FairValueOfDerivativeLiabilitiesSubjectToCrossDefaultProvisions_01289F0892913747E235F8A4D0B73239" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CollateralAlreadyPostedAggregateFairValue" xlink:label="loc_us-gaap_CollateralAlreadyPostedAggregateFairValue_CB7E063CD1FF00FAA402F8A4D0B7D12B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CollateralTriggeringEventsAbstract_6B866E4F9737DE7B5A26F8A4D0B76081" xlink:to="loc_us-gaap_CollateralAlreadyPostedAggregateFairValue_CB7E063CD1FF00FAA402F8A4D0B7D12B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetsNeededForImmediateSettlementAggregateFairValue" xlink:label="loc_us-gaap_AssetsNeededForImmediateSettlementAggregateFairValue_AE18DF139A8D59346884F8A4D0B75E99" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CollateralTriggeringEventsAbstract_6B866E4F9737DE7B5A26F8A4D0B76081" xlink:to="loc_us-gaap_AssetsNeededForImmediateSettlementAggregateFairValue_AE18DF139A8D59346884F8A4D0B75E99" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_DerivativesAndHedgingTextualsAbstract" xlink:label="loc_aep_DerivativesAndHedgingTextualsAbstract_973967F93CFE6C157D79F8A4D0B7F34D" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_2A2AE0840F203DCAA273F8A4D0AE9EBA" xlink:to="loc_aep_DerivativesAndHedgingTextualsAbstract_973967F93CFE6C157D79F8A4D0B7F34D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MaximumLengthOfTimeHedgedInPriceRiskCashFlowHedge1" xlink:label="loc_us-gaap_MaximumLengthOfTimeHedgedInPriceRiskCashFlowHedge1_3BB9866F457D4DD37FB2F8A4D0B81703" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_DerivativesAndHedgingTextualsAbstract_973967F93CFE6C157D79F8A4D0B7F34D" xlink:to="loc_us-gaap_MaximumLengthOfTimeHedgedInPriceRiskCashFlowHedge1_3BB9866F457D4DD37FB2F8A4D0B81703" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_CrossDefaultProvisionsMaximumThirdPartyObligationAmount" xlink:label="loc_aep_CrossDefaultProvisionsMaximumThirdPartyObligationAmount_FB6F70E8B511A5399AB4F8A4D0B8FE4C" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_DerivativesAndHedgingTextualsAbstract_973967F93CFE6C157D79F8A4D0B7F34D" xlink:to="loc_aep_CrossDefaultProvisionsMaximumThirdPartyObligationAmount_FB6F70E8B511A5399AB4F8A4D0B8FE4C" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/DerivativesAndHedgingPolicies" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_76CB58F4B095726BABDF8751A77B742D" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_29E30486069598A7FB128751A77BDF20" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_76CB58F4B095726BABDF8751A77B742D" xlink:to="loc_us-gaap_StatementTable_29E30486069598A7FB128751A77BDF20" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_50E2200DE38492998CA98751A77B6EB9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_29E30486069598A7FB128751A77BDF20" xlink:to="loc_dei_LegalEntityAxis_50E2200DE38492998CA98751A77B6EB9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_3216CB217DBF2C5D40338751A77BC52A_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_50E2200DE38492998CA98751A77B6EB9" xlink:to="loc_dei_EntityDomain_3216CB217DBF2C5D40338751A77BC52A_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_3216CB217DBF2C5D40338751A77BC52A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_50E2200DE38492998CA98751A77B6EB9" xlink:to="loc_dei_EntityDomain_3216CB217DBF2C5D40338751A77BC52A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativesPolicyTextBlock" xlink:label="loc_us-gaap_DerivativesPolicyTextBlock_2C091824E21C9E0793928751A77B45B8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_76CB58F4B095726BABDF8751A77B742D" xlink:to="loc_us-gaap_DerivativesPolicyTextBlock_2C091824E21C9E0793928751A77B45B8" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/DerivativesAndHedgingTables" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_E1CD965B8E233BCCC234C007A5890362" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_981985B369DDE61D6201C007A589D494" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_E1CD965B8E233BCCC234C007A5890362" xlink:to="loc_us-gaap_StatementTable_981985B369DDE61D6201C007A589D494" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_F5B4C07C3B508D2360ACC007A589C4F5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_981985B369DDE61D6201C007A589D494" xlink:to="loc_dei_LegalEntityAxis_F5B4C07C3B508D2360ACC007A589C4F5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_2A1EF10685D4044E8685C007A589558B_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_F5B4C07C3B508D2360ACC007A589C4F5" xlink:to="loc_dei_EntityDomain_2A1EF10685D4044E8685C007A589558B_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_2A1EF10685D4044E8685C007A589558B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_F5B4C07C3B508D2360ACC007A589C4F5" xlink:to="loc_dei_EntityDomain_2A1EF10685D4044E8685C007A589558B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfDerivativeInstrumentsGainLossInStatementOfFinancialPerformanceTextBlock" xlink:label="loc_us-gaap_ScheduleOfDerivativeInstrumentsGainLossInStatementOfFinancialPerformanceTextBlock_75A0197EED6C0EAC9019C009EBC6EF0B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E1CD965B8E233BCCC234C007A5890362" xlink:to="loc_us-gaap_ScheduleOfDerivativeInstrumentsGainLossInStatementOfFinancialPerformanceTextBlock_75A0197EED6C0EAC9019C009EBC6EF0B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfNotionalAmountsOfOutstandingDerivativePositionsTableTextBlock" xlink:label="loc_us-gaap_ScheduleOfNotionalAmountsOfOutstandingDerivativePositionsTableTextBlock_3942ABEBFBB0F80F2905C007A58967D7" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E1CD965B8E233BCCC234C007A5890362" xlink:to="loc_us-gaap_ScheduleOfNotionalAmountsOfOutstandingDerivativePositionsTableTextBlock_3942ABEBFBB0F80F2905C007A58967D7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfDerivativeInstrumentsInStatementOfFinancialPositionFairValueTextBlock" xlink:label="loc_us-gaap_ScheduleOfDerivativeInstrumentsInStatementOfFinancialPositionFairValueTextBlock_8A23AEFBA29A0B97325DC007A58AB31C" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E1CD965B8E233BCCC234C007A5890362" xlink:to="loc_us-gaap_ScheduleOfDerivativeInstrumentsInStatementOfFinancialPositionFairValueTextBlock_8A23AEFBA29A0B97325DC007A58AB31C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfDerivativeInstrumentsIncludedInTradingActivitiesTextBlock" xlink:label="loc_us-gaap_ScheduleOfDerivativeInstrumentsIncludedInTradingActivitiesTextBlock_99D8D212A785FB45DEE8C007A58AF5E2" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E1CD965B8E233BCCC234C007A5890362" xlink:to="loc_us-gaap_ScheduleOfDerivativeInstrumentsIncludedInTradingActivitiesTextBlock_99D8D212A785FB45DEE8C007A58AF5E2" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ImpactOfCashFlowHedgesOnBalanceSheetTextBlock" xlink:label="loc_aep_ImpactOfCashFlowHedgesOnBalanceSheetTextBlock_20429CD847C1EC302E44C007A58A0F8C" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E1CD965B8E233BCCC234C007A5890362" xlink:to="loc_aep_ImpactOfCashFlowHedgesOnBalanceSheetTextBlock_20429CD847C1EC302E44C007A58A0F8C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_CrossDefaultProvisionTextBlock" xlink:label="loc_aep_CrossDefaultProvisionTextBlock_308D11FAC10F7245806BC007A58A153D" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E1CD965B8E233BCCC234C007A5890362" xlink:to="loc_aep_CrossDefaultProvisionTextBlock_308D11FAC10F7245806BC007A58A153D" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/DispositionsAndImpairments" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_5C70647ABD1168DBEE46F30C2D4A1992" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_BF48981DD16B3448403AF30C2D4965AE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_5C70647ABD1168DBEE46F30C2D4A1992" xlink:to="loc_us-gaap_StatementTable_BF48981DD16B3448403AF30C2D4965AE" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_8297326E58FF4AF0C4D4F30C2D49C9DE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_BF48981DD16B3448403AF30C2D4965AE" xlink:to="loc_dei_LegalEntityAxis_8297326E58FF4AF0C4D4F30C2D49C9DE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_D86F8B1492DDD4BDD84EF30C2D4A9905_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_8297326E58FF4AF0C4D4F30C2D49C9DE" xlink:to="loc_dei_EntityDomain_D86F8B1492DDD4BDD84EF30C2D4A9905_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_D86F8B1492DDD4BDD84EF30C2D4A9905" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_8297326E58FF4AF0C4D4F30C2D49C9DE" xlink:to="loc_dei_EntityDomain_D86F8B1492DDD4BDD84EF30C2D4A9905" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsDisclosureTextBlock" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsDisclosureTextBlock_C285EC389D7154DCCEFBF30C2D4AA3FA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_5C70647ABD1168DBEE46F30C2D4A1992" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsDisclosureTextBlock_C285EC389D7154DCCEFBF30C2D4AA3FA" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/DispositionsAndImpairmentsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_C57602B68E869013E6B9F7E8BFA0BF6B" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_A8ECA64B91843EEF6290F7E8BFA05C69" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_C57602B68E869013E6B9F7E8BFA0BF6B" xlink:to="loc_us-gaap_StatementTable_A8ECA64B91843EEF6290F7E8BFA05C69" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PublicUtilityAxis" xlink:label="loc_us-gaap_PublicUtilityAxis_7CDEC687319A32538C0AF7E8BFA0563A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_A8ECA64B91843EEF6290F7E8BFA05C69" xlink:to="loc_us-gaap_PublicUtilityAxis_7CDEC687319A32538C0AF7E8BFA0563A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_UtilityPlantDomain" xlink:label="loc_us-gaap_UtilityPlantDomain_0B1D4F0AC4436B7AFC1BF7E8BFA06702_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PublicUtilityAxis_7CDEC687319A32538C0AF7E8BFA0563A" xlink:to="loc_us-gaap_UtilityPlantDomain_0B1D4F0AC4436B7AFC1BF7E8BFA06702_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_UtilityPlantDomain" xlink:label="loc_us-gaap_UtilityPlantDomain_0B1D4F0AC4436B7AFC1BF7E8BFA06702" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PublicUtilityAxis_7CDEC687319A32538C0AF7E8BFA0563A" xlink:to="loc_us-gaap_UtilityPlantDomain_0B1D4F0AC4436B7AFC1BF7E8BFA06702" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_GavinWaterfordDarbyandLawrenceburgPlantsMember" xlink:label="loc_aep_GavinWaterfordDarbyandLawrenceburgPlantsMember_10A9AEC387ED1A95ED20F7E8BFA09486" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_UtilityPlantDomain_0B1D4F0AC4436B7AFC1BF7E8BFA06702" xlink:to="loc_aep_GavinWaterfordDarbyandLawrenceburgPlantsMember_10A9AEC387ED1A95ED20F7E8BFA09486" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ImpairedLongLivedAssetsHeldAndUsedByTypeAxis" xlink:label="loc_us-gaap_ImpairedLongLivedAssetsHeldAndUsedByTypeAxis_2F8BA3664BD55C946EFDF7E8BFA0C0DF" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_A8ECA64B91843EEF6290F7E8BFA05C69" xlink:to="loc_us-gaap_ImpairedLongLivedAssetsHeldAndUsedByTypeAxis_2F8BA3664BD55C946EFDF7E8BFA0C0DF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ImpairedLongLivedAssetsHeldAndUsedAssetNameDomain" xlink:label="loc_us-gaap_ImpairedLongLivedAssetsHeldAndUsedAssetNameDomain_8AF8A5814DB532B1071EF7E8BFA0529E_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ImpairedLongLivedAssetsHeldAndUsedByTypeAxis_2F8BA3664BD55C946EFDF7E8BFA0C0DF" xlink:to="loc_us-gaap_ImpairedLongLivedAssetsHeldAndUsedAssetNameDomain_8AF8A5814DB532B1071EF7E8BFA0529E_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ImpairedLongLivedAssetsHeldAndUsedAssetNameDomain" xlink:label="loc_us-gaap_ImpairedLongLivedAssetsHeldAndUsedAssetNameDomain_8AF8A5814DB532B1071EF7E8BFA0529E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ImpairedLongLivedAssetsHeldAndUsedByTypeAxis_2F8BA3664BD55C946EFDF7E8BFA0C0DF" xlink:to="loc_us-gaap_ImpairedLongLivedAssetsHeldAndUsedAssetNameDomain_8AF8A5814DB532B1071EF7E8BFA0529E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherAssetsMember" xlink:label="loc_us-gaap_OtherAssetsMember_C00D4BD399940F678939F7E8BFA00924" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ImpairedLongLivedAssetsHeldAndUsedAssetNameDomain_8AF8A5814DB532B1071EF7E8BFA0529E" xlink:to="loc_us-gaap_OtherAssetsMember_C00D4BD399940F678939F7E8BFA00924" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MerchantCoalFiredGenerationAssetsMember" xlink:label="loc_aep_MerchantCoalFiredGenerationAssetsMember_C33AAE3E01AD58CD614EF7E8BFA02B96" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ImpairedLongLivedAssetsHeldAndUsedAssetNameDomain_8AF8A5814DB532B1071EF7E8BFA0529E" xlink:to="loc_aep_MerchantCoalFiredGenerationAssetsMember_C33AAE3E01AD58CD614EF7E8BFA02B96" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ZimmerPlantAssetsMember" xlink:label="loc_aep_ZimmerPlantAssetsMember_713501DAAE77D5F54881F7E8BFA0F913" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ImpairedLongLivedAssetsHeldAndUsedAssetNameDomain_8AF8A5814DB532B1071EF7E8BFA0529E" xlink:to="loc_aep_ZimmerPlantAssetsMember_713501DAAE77D5F54881F7E8BFA0F913" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_031FBED11EE82A1A7C4DF7E8BFA017AF" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_A8ECA64B91843EEF6290F7E8BFA05C69" xlink:to="loc_dei_LegalEntityAxis_031FBED11EE82A1A7C4DF7E8BFA017AF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_B656E9BCF568A36D48B2F7E8BFA0A603_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_031FBED11EE82A1A7C4DF7E8BFA017AF" xlink:to="loc_dei_EntityDomain_B656E9BCF568A36D48B2F7E8BFA0A603_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_B656E9BCF568A36D48B2F7E8BFA0A603" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_031FBED11EE82A1A7C4DF7E8BFA017AF" xlink:to="loc_dei_EntityDomain_B656E9BCF568A36D48B2F7E8BFA0A603" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_82FBC60456442D6B9A01F7E8BFA0D8B2" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_A8ECA64B91843EEF6290F7E8BFA05C69" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_82FBC60456442D6B9A01F7E8BFA0D8B2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_C5E1C242773329E71F5EF7E8BFA0A806_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_82FBC60456442D6B9A01F7E8BFA0D8B2" xlink:to="loc_us-gaap_SegmentDomain_C5E1C242773329E71F5EF7E8BFA0A806_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_C5E1C242773329E71F5EF7E8BFA0A806" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_82FBC60456442D6B9A01F7E8BFA0D8B2" xlink:to="loc_us-gaap_SegmentDomain_C5E1C242773329E71F5EF7E8BFA0A806" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_GenerationAndMarketingMember" xlink:label="loc_aep_GenerationAndMarketingMember_4243758BAD2A71C82BD2F7E8BFA05EA2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_C5E1C242773329E71F5EF7E8BFA0A806" xlink:to="loc_aep_GenerationAndMarketingMember_4243758BAD2A71C82BD2F7E8BFA05EA2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CorporateAndOtherMember" xlink:label="loc_us-gaap_CorporateAndOtherMember_1913906F0F58E1241DB9F7E8BFA00285" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_C5E1C242773329E71F5EF7E8BFA0A806" xlink:to="loc_us-gaap_CorporateAndOtherMember_1913906F0F58E1241DB9F7E8BFA00285" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromSalesOfAssetsInvestingActivities" xlink:label="loc_us-gaap_ProceedsFromSalesOfAssetsInvestingActivities_D411CB3047C7EA2ACA5BF7E8BFA0EDF1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_C57602B68E869013E6B9F7E8BFA0BF6B" xlink:to="loc_us-gaap_ProceedsFromSalesOfAssetsInvestingActivities_D411CB3047C7EA2ACA5BF7E8BFA0EDF1" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_CashProceedsfromDispositionofBusinessNet" xlink:label="loc_aep_CashProceedsfromDispositionofBusinessNet_977C89E6FCFCC83DB42EF7E8BFA0B49E" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_C57602B68E869013E6B9F7E8BFA0BF6B" xlink:to="loc_aep_CashProceedsfromDispositionofBusinessNet_977C89E6FCFCC83DB42EF7E8BFA0B49E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal" xlink:label="loc_us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal_DA387F42599A39150303F7E8BFA05384" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_C57602B68E869013E6B9F7E8BFA0BF6B" xlink:to="loc_us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal_DA387F42599A39150303F7E8BFA05384" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_UtilitiesOperatingExpenseOperations" xlink:label="loc_us-gaap_UtilitiesOperatingExpenseOperations_BD9A1734428C116B8F66F7E8BFA0F038" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_C57602B68E869013E6B9F7E8BFA0BF6B" xlink:to="loc_us-gaap_UtilitiesOperatingExpenseOperations_BD9A1734428C116B8F66F7E8BFA0F038" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaximumPotentialLossRelatedToGuarantee" xlink:label="loc_aep_MaximumPotentialLossRelatedToGuarantee_301372A9351640389664F7E8BFA0563F" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_C57602B68E869013E6B9F7E8BFA0BF6B" xlink:to="loc_aep_MaximumPotentialLossRelatedToGuarantee_301372A9351640389664F7E8BFA0563F" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/DispositionsAndImpairmentsTables" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_96C6F64B3A7240E6BD14F7E8BFB03213" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_782DAD68E7D3422C11DDF7E8BFB092DA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_96C6F64B3A7240E6BD14F7E8BFB03213" xlink:to="loc_us-gaap_StatementTable_782DAD68E7D3422C11DDF7E8BFB092DA" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_573C311A7AC774CB1A85F7E8BFB0280C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_782DAD68E7D3422C11DDF7E8BFB092DA" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_573C311A7AC774CB1A85F7E8BFB0280C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_E7A38D2438D38E8BD3DFF7E8BFB084E7_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_573C311A7AC774CB1A85F7E8BFB0280C" xlink:to="loc_us-gaap_SegmentDomain_E7A38D2438D38E8BD3DFF7E8BFB084E7_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_E7A38D2438D38E8BD3DFF7E8BFB084E7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_573C311A7AC774CB1A85F7E8BFB0280C" xlink:to="loc_us-gaap_SegmentDomain_E7A38D2438D38E8BD3DFF7E8BFB084E7" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_GenerationAndMarketingMember" xlink:label="loc_aep_GenerationAndMarketingMember_DB38231B12A0696B6A90F7E8BFB0E3CC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_E7A38D2438D38E8BD3DFF7E8BFB084E7" xlink:to="loc_aep_GenerationAndMarketingMember_DB38231B12A0696B6A90F7E8BFB0E3CC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_EC72835293BC12229108F7E8BFB055B1" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_782DAD68E7D3422C11DDF7E8BFB092DA" xlink:to="loc_dei_LegalEntityAxis_EC72835293BC12229108F7E8BFB055B1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_1505DA8313763B12B1E4F7E8BFB0B8AF_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_EC72835293BC12229108F7E8BFB055B1" xlink:to="loc_dei_EntityDomain_1505DA8313763B12B1E4F7E8BFB0B8AF_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_1505DA8313763B12B1E4F7E8BFB0B8AF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_EC72835293BC12229108F7E8BFB055B1" xlink:to="loc_dei_EntityDomain_1505DA8313763B12B1E4F7E8BFB0B8AF" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/DocumentAndEntityInformation" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_757CFED87D35F5346015907583199C0B" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntitiesTable" xlink:label="loc_dei_EntitiesTable_BBEF61B4EE597DE5C9F1907583170596" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_757CFED87D35F5346015907583199C0B" xlink:to="loc_dei_EntitiesTable_BBEF61B4EE597DE5C9F1907583170596" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_D86219F00671C9B4A71B9075831893EB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_BBEF61B4EE597DE5C9F1907583170596" xlink:to="loc_dei_LegalEntityAxis_D86219F00671C9B4A71B9075831893EB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_17D2884D3AC7C56254B0907583185278_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_D86219F00671C9B4A71B9075831893EB" xlink:to="loc_dei_EntityDomain_17D2884D3AC7C56254B0907583185278_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_17D2884D3AC7C56254B0907583185278" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_D86219F00671C9B4A71B9075831893EB" xlink:to="loc_dei_EntityDomain_17D2884D3AC7C56254B0907583185278" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTexasInc.Member" xlink:label="loc_aep_AEPTexasInc.Member_AE91DEA788EB1A539E7B9075831841FE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_17D2884D3AC7C56254B0907583185278" xlink:to="loc_aep_AEPTexasInc.Member_AE91DEA788EB1A539E7B9075831841FE" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTransmissionCoMember" xlink:label="loc_aep_AEPTransmissionCoMember_5A72EE3C38BAEE2F9F5090758319A980" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_17D2884D3AC7C56254B0907583185278" xlink:to="loc_aep_AEPTransmissionCoMember_5A72EE3C38BAEE2F9F5090758319A980" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AppalachianPowerCoMember" xlink:label="loc_aep_AppalachianPowerCoMember_B9EAD9A3E6D94684A7609075831925F6" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_17D2884D3AC7C56254B0907583185278" xlink:to="loc_aep_AppalachianPowerCoMember_B9EAD9A3E6D94684A7609075831925F6" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IndianaMichiganPowerCoMember" xlink:label="loc_aep_IndianaMichiganPowerCoMember_B0D376E220B92B70194690758319CEC3" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_17D2884D3AC7C56254B0907583185278" xlink:to="loc_aep_IndianaMichiganPowerCoMember_B0D376E220B92B70194690758319CEC3" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OhioPowerCoMember" xlink:label="loc_aep_OhioPowerCoMember_2F189D6794DD847331C790758319E356" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_17D2884D3AC7C56254B0907583185278" xlink:to="loc_aep_OhioPowerCoMember_2F189D6794DD847331C790758319E356" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_PublicServiceCoOfOklahomaMember" xlink:label="loc_aep_PublicServiceCoOfOklahomaMember_C8C2A67A575F0717F30290758319AB00" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_17D2884D3AC7C56254B0907583185278" xlink:to="loc_aep_PublicServiceCoOfOklahomaMember_C8C2A67A575F0717F30290758319AB00" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SouthwesternElectricPowerCoMember" xlink:label="loc_aep_SouthwesternElectricPowerCoMember_A4613280803866A5546490758319273F" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_17D2884D3AC7C56254B0907583185278" xlink:to="loc_aep_SouthwesternElectricPowerCoMember_A4613280803866A5546490758319273F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityRegistrantName" xlink:label="loc_dei_EntityRegistrantName_9D80617AA058C8C44C38907583191944" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_757CFED87D35F5346015907583199C0B" xlink:to="loc_dei_EntityRegistrantName_9D80617AA058C8C44C38907583191944" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityCentralIndexKey" xlink:label="loc_dei_EntityCentralIndexKey_186869CEC6DF6311066C90758319342F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_757CFED87D35F5346015907583199C0B" xlink:to="loc_dei_EntityCentralIndexKey_186869CEC6DF6311066C90758319342F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_DocumentType" xlink:label="loc_dei_DocumentType_6671716191CADB6D66C290758319EFB0" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_757CFED87D35F5346015907583199C0B" xlink:to="loc_dei_DocumentType_6671716191CADB6D66C290758319EFB0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_DocumentPeriodEndDate" xlink:label="loc_dei_DocumentPeriodEndDate_9E041BD9BFBC6205A80B907583197862" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_757CFED87D35F5346015907583199C0B" xlink:to="loc_dei_DocumentPeriodEndDate_9E041BD9BFBC6205A80B907583197862" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_AmendmentFlag" xlink:label="loc_dei_AmendmentFlag_B7C6B7E0CB51202BA80190758319D010" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_757CFED87D35F5346015907583199C0B" xlink:to="loc_dei_AmendmentFlag_B7C6B7E0CB51202BA80190758319D010" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_DocumentFiscalYearFocus" xlink:label="loc_dei_DocumentFiscalYearFocus_038A65935FBE4B2453E09075831A566A" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_757CFED87D35F5346015907583199C0B" xlink:to="loc_dei_DocumentFiscalYearFocus_038A65935FBE4B2453E09075831A566A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_DocumentFiscalPeriodFocus" xlink:label="loc_dei_DocumentFiscalPeriodFocus_D822D7A26F71AFBBEC0A9075831A5A86" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_757CFED87D35F5346015907583199C0B" xlink:to="loc_dei_DocumentFiscalPeriodFocus_D822D7A26F71AFBBEC0A9075831A5A86" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_CurrentFiscalYearEndDate" xlink:label="loc_dei_CurrentFiscalYearEndDate_49BEE8AE2D344DD6EAB89075831ADE13" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_757CFED87D35F5346015907583199C0B" xlink:to="loc_dei_CurrentFiscalYearEndDate_49BEE8AE2D344DD6EAB89075831ADE13" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityFilerCategory" xlink:label="loc_dei_EntityFilerCategory_9BC16F0B4F3F5B92F3179075831A2084" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_757CFED87D35F5346015907583199C0B" xlink:to="loc_dei_EntityFilerCategory_9BC16F0B4F3F5B92F3179075831A2084" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityCommonStockSharesOutstanding" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_90DED176D22AE51E8BD79075831A3F91" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_757CFED87D35F5346015907583199C0B" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_90DED176D22AE51E8BD79075831A3F91" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/FairValueAssetsAndLiabilitiesDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_F5398FA086C08DF0015BFE22F835B585" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_2E6CE755EC0141647B83FE22F82FDF23" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_F5398FA086C08DF0015BFE22F835B585" xlink:to="loc_us-gaap_StatementTable_2E6CE755EC0141647B83FE22F82FDF23" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_71E693EA3A0FB2988FA6FE22F82F687D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_2E6CE755EC0141647B83FE22F82FDF23" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_71E693EA3A0FB2988FA6FE22F82F687D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_E8907278521ACD3B8664FE22F82F3D2F_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_71E693EA3A0FB2988FA6FE22F82F687D" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_E8907278521ACD3B8664FE22F82F3D2F_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_E8907278521ACD3B8664FE22F82F3D2F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_71E693EA3A0FB2988FA6FE22F82F687D" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_E8907278521ACD3B8664FE22F82F3D2F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashMember" xlink:label="loc_us-gaap_CashMember_FB60BC6CAE56EF386BCAFE22F82F2BE9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_E8907278521ACD3B8664FE22F82F3D2F" xlink:to="loc_us-gaap_CashMember_FB60BC6CAE56EF386BCAFE22F82F2BE9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FixedIncomeFundsMember" xlink:label="loc_us-gaap_FixedIncomeFundsMember_2F89758A7E016C644DF0FE22F82F94E0" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_E8907278521ACD3B8664FE22F82F3D2F" xlink:to="loc_us-gaap_FixedIncomeFundsMember_2F89758A7E016C644DF0FE22F82F94E0" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MutualFundsFixedIncomeMember" xlink:label="loc_aep_MutualFundsFixedIncomeMember_8D1B99FD556E1D06FC4CFE22F82F76D7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FixedIncomeFundsMember_2F89758A7E016C644DF0FE22F82F94E0" xlink:to="loc_aep_MutualFundsFixedIncomeMember_8D1B99FD556E1D06FC4CFE22F82F76D7" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MutualFundsEquityMember" xlink:label="loc_aep_MutualFundsEquityMember_54E82D7F26DF87B82F87FE22F82FB7F7" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_E8907278521ACD3B8664FE22F82F3D2F" xlink:to="loc_aep_MutualFundsEquityMember_54E82D7F26DF87B82F87FE22F82FB7F7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashAndCashEquivalentsMember" xlink:label="loc_us-gaap_CashAndCashEquivalentsMember_F01F66FA56438EDD6B76FE22F82F81BB" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_E8907278521ACD3B8664FE22F82F3D2F" xlink:to="loc_us-gaap_CashAndCashEquivalentsMember_F01F66FA56438EDD6B76FE22F82F81BB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_76C51BF16839758907DCFE22F830B9E0" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_E8907278521ACD3B8664FE22F82F3D2F" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_76C51BF16839758907DCFE22F830B9E0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CorporateDebtSecuritiesMember" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_D6B3DEE56E26BA8A93BEFE22F83051A0" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_E8907278521ACD3B8664FE22F82F3D2F" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_D6B3DEE56E26BA8A93BEFE22F83051A0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StateAndLocalJurisdictionMember" xlink:label="loc_us-gaap_StateAndLocalJurisdictionMember_0EB8F86B286707D1466CFE22F8317139" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_E8907278521ACD3B8664FE22F82F3D2F" xlink:to="loc_us-gaap_StateAndLocalJurisdictionMember_0EB8F86B286707D1466CFE22F8317139" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_DomesticMember" xlink:label="loc_aep_DomesticMember_96576EDC5FA4560D97E5FE22F831DB6B" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_E8907278521ACD3B8664FE22F82F3D2F" xlink:to="loc_aep_DomesticMember_96576EDC5FA4560D97E5FE22F831DB6B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_05B0C7EEC88B4486F6E5FE22F83104F7" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_2E6CE755EC0141647B83FE22F82FDF23" xlink:to="loc_dei_LegalEntityAxis_05B0C7EEC88B4486F6E5FE22F83104F7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_E67D2D1BB0FF36C867DAFE22F831DB3C_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_05B0C7EEC88B4486F6E5FE22F83104F7" xlink:to="loc_dei_EntityDomain_E67D2D1BB0FF36C867DAFE22F831DB3C_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_E67D2D1BB0FF36C867DAFE22F831DB3C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_05B0C7EEC88B4486F6E5FE22F83104F7" xlink:to="loc_dei_EntityDomain_E67D2D1BB0FF36C867DAFE22F831DB3C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTexasInc.Member" xlink:label="loc_aep_AEPTexasInc.Member_D1A9CFC27BB385E2C5BCFE22F831A581" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_E67D2D1BB0FF36C867DAFE22F831DB3C" xlink:to="loc_aep_AEPTexasInc.Member_D1A9CFC27BB385E2C5BCFE22F831A581" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AppalachianPowerCoMember" xlink:label="loc_aep_AppalachianPowerCoMember_0DBBA8AF8AE969D8E404FE22F831698D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_E67D2D1BB0FF36C867DAFE22F831DB3C" xlink:to="loc_aep_AppalachianPowerCoMember_0DBBA8AF8AE969D8E404FE22F831698D" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IndianaMichiganPowerCoMember" xlink:label="loc_aep_IndianaMichiganPowerCoMember_D1F0AB16EC4D887CCB44FE22F831966E" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_E67D2D1BB0FF36C867DAFE22F831DB3C" xlink:to="loc_aep_IndianaMichiganPowerCoMember_D1F0AB16EC4D887CCB44FE22F831966E" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OhioPowerCoMember" xlink:label="loc_aep_OhioPowerCoMember_7E5C9EC0C41324AE331AFE22F83147D3" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_E67D2D1BB0FF36C867DAFE22F831DB3C" xlink:to="loc_aep_OhioPowerCoMember_7E5C9EC0C41324AE331AFE22F83147D3" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_PublicServiceCoOfOklahomaMember" xlink:label="loc_aep_PublicServiceCoOfOklahomaMember_8422FB00EAF59DFBCFCBFE22F8316643" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_E67D2D1BB0FF36C867DAFE22F831DB3C" xlink:to="loc_aep_PublicServiceCoOfOklahomaMember_8422FB00EAF59DFBCFCBFE22F8316643" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SouthwesternElectricPowerCoMember" xlink:label="loc_aep_SouthwesternElectricPowerCoMember_CFBAEA6448880CDC7ADFFE22F831463C" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_E67D2D1BB0FF36C867DAFE22F831DB3C" xlink:to="loc_aep_SouthwesternElectricPowerCoMember_CFBAEA6448880CDC7ADFFE22F831463C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_59611DA34EE7D72A7047FE22F83212CB" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_2E6CE755EC0141647B83FE22F82FDF23" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_59611DA34EE7D72A7047FE22F83212CB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_HedgingRelationshipDomain" xlink:label="loc_us-gaap_HedgingRelationshipDomain_82A68B9166EDB7D691B7FE22F8321A02_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_59611DA34EE7D72A7047FE22F83212CB" xlink:to="loc_us-gaap_HedgingRelationshipDomain_82A68B9166EDB7D691B7FE22F8321A02_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_HedgingRelationshipDomain" xlink:label="loc_us-gaap_HedgingRelationshipDomain_82A68B9166EDB7D691B7FE22F8321A02" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_59611DA34EE7D72A7047FE22F83212CB" xlink:to="loc_us-gaap_HedgingRelationshipDomain_82A68B9166EDB7D691B7FE22F8321A02" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RiskManagementCommodityContractsMember" xlink:label="loc_aep_RiskManagementCommodityContractsMember_D370DE5A6C67EFBBE88AFE22F8321BAA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_82A68B9166EDB7D691B7FE22F8321A02" xlink:to="loc_aep_RiskManagementCommodityContractsMember_D370DE5A6C67EFBBE88AFE22F8321BAA" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_EnergyContractsMember" xlink:label="loc_aep_EnergyContractsMember_7E2B58CD4B1BD1976320FE22F832D470" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_RiskManagementCommodityContractsMember_D370DE5A6C67EFBBE88AFE22F8321BAA" xlink:to="loc_aep_EnergyContractsMember_7E2B58CD4B1BD1976320FE22F832D470" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_NaturalGasContractMember" xlink:label="loc_aep_NaturalGasContractMember_834549FA7EEFA23E9D94FE22F8325D8A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_RiskManagementCommodityContractsMember_D370DE5A6C67EFBBE88AFE22F8321BAA" xlink:to="loc_aep_NaturalGasContractMember_834549FA7EEFA23E9D94FE22F8325D8A" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_FinancialTrasnsmissionRightsMember" xlink:label="loc_aep_FinancialTrasnsmissionRightsMember_0B3C5122B01A72C31548FE22F8331503" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_RiskManagementCommodityContractsMember_D370DE5A6C67EFBBE88AFE22F8321BAA" xlink:to="loc_aep_FinancialTrasnsmissionRightsMember_0B3C5122B01A72C31548FE22F8331503" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommodityMember" xlink:label="loc_us-gaap_CommodityMember_FAE09BB5DB1000771DFFFE22F833C7F0" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_82A68B9166EDB7D691B7FE22F8321A02" xlink:to="loc_us-gaap_CommodityMember_FAE09BB5DB1000771DFFFE22F833C7F0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueHedgingMember" xlink:label="loc_us-gaap_FairValueHedgingMember_AE8CF043C1D4265F8310FE22F8339819" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_82A68B9166EDB7D691B7FE22F8321A02" xlink:to="loc_us-gaap_FairValueHedgingMember_AE8CF043C1D4265F8310FE22F8339819" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaturityOfFairValueRiskManagementContractsAxis" xlink:label="loc_aep_MaturityOfFairValueRiskManagementContractsAxis_594A395BBE6482115457FE22F8334508" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_2E6CE755EC0141647B83FE22F82FDF23" xlink:to="loc_aep_MaturityOfFairValueRiskManagementContractsAxis_594A395BBE6482115457FE22F8334508" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaturityYearDomain" xlink:label="loc_aep_MaturityYearDomain_BA49A27D3449655291A6FE22F8339857_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_aep_MaturityOfFairValueRiskManagementContractsAxis_594A395BBE6482115457FE22F8334508" xlink:to="loc_aep_MaturityYearDomain_BA49A27D3449655291A6FE22F8339857_default" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaturityYearDomain" xlink:label="loc_aep_MaturityYearDomain_BA49A27D3449655291A6FE22F8339857" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_aep_MaturityOfFairValueRiskManagementContractsAxis_594A395BBE6482115457FE22F8334508" xlink:to="loc_aep_MaturityYearDomain_BA49A27D3449655291A6FE22F8339857" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_WithinCurrentYearMember" xlink:label="loc_aep_WithinCurrentYearMember_B4027C6220A9BCB97E09FE22F833C926" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_MaturityYearDomain_BA49A27D3449655291A6FE22F8339857" xlink:to="loc_aep_WithinCurrentYearMember_B4027C6220A9BCB97E09FE22F833C926" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaturityPeriod2Member" xlink:label="loc_aep_MaturityPeriod2Member_38571C8B2E35733E4CB5FE22F8343D1D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_MaturityYearDomain_BA49A27D3449655291A6FE22F8339857" xlink:to="loc_aep_MaturityPeriod2Member_38571C8B2E35733E4CB5FE22F8343D1D" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaturityPeriod3Member" xlink:label="loc_aep_MaturityPeriod3Member_68463A575E4B18F66E5DFE22F834AC2A" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_MaturityYearDomain_BA49A27D3449655291A6FE22F8339857" xlink:to="loc_aep_MaturityPeriod3Member_68463A575E4B18F66E5DFE22F834AC2A" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaturityPeriodFourMember" xlink:label="loc_aep_MaturityPeriodFourMember_687B67485D8343F9D608FE22F8348355" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_MaturityYearDomain_BA49A27D3449655291A6FE22F8339857" xlink:to="loc_aep_MaturityPeriodFourMember_687B67485D8343F9D608FE22F8348355" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_DD9CC00BCE4835F1A601FE22F8349474" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_2E6CE755EC0141647B83FE22F82FDF23" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_DD9CC00BCE4835F1A601FE22F8349474" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_864E012EDFA945254D49FE22F834635C_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_DD9CC00BCE4835F1A601FE22F8349474" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_864E012EDFA945254D49FE22F834635C_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_864E012EDFA945254D49FE22F834635C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_DD9CC00BCE4835F1A601FE22F8349474" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_864E012EDFA945254D49FE22F834635C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_7C61A64CF0EB15CBC493FE22F8344841" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_864E012EDFA945254D49FE22F834635C" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_7C61A64CF0EB15CBC493FE22F8344841" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_DADCC131CAC87507BB34FE22F8349768" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_864E012EDFA945254D49FE22F834635C" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_DADCC131CAC87507BB34FE22F8349768" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_E895BFAC9486BEB487E4FE22F834852B" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_864E012EDFA945254D49FE22F834635C" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_E895BFAC9486BEB487E4FE22F834852B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueByMeasurementBasisAxis" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_E9E0EB9233BF7A241C94FE22F834B6C5" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_2E6CE755EC0141647B83FE22F82FDF23" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_E9E0EB9233BF7A241C94FE22F834B6C5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_35FA24ED08557787EC3EFE22F83406AD_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_E9E0EB9233BF7A241C94FE22F834B6C5" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_35FA24ED08557787EC3EFE22F83406AD_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueDisclosureItemAmountsDomain" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_A5ECC8E87670AC2BB196FE22F834D647" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_E9E0EB9233BF7A241C94FE22F834B6C5" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_A5ECC8E87670AC2BB196FE22F834D647" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_35FA24ED08557787EC3EFE22F83406AD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_A5ECC8E87670AC2BB196FE22F834D647" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_35FA24ED08557787EC3EFE22F83406AD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PortionAtOtherThanFairValueFairValueDisclosureMember" xlink:label="loc_us-gaap_PortionAtOtherThanFairValueFairValueDisclosureMember_C436C78E570C37AA3AD3FE22F835DE85" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_A5ECC8E87670AC2BB196FE22F834D647" xlink:to="loc_us-gaap_PortionAtOtherThanFairValueFairValueDisclosureMember_C436C78E570C37AA3AD3FE22F835DE85" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_5096A6DA8A3E77C7AF2BFE22F83588B5" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_2E6CE755EC0141647B83FE22F82FDF23" xlink:to="loc_us-gaap_RangeAxis_5096A6DA8A3E77C7AF2BFE22F83588B5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_F37E3FE62E20824123BDFE22F83514FA_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_5096A6DA8A3E77C7AF2BFE22F83588B5" xlink:to="loc_us-gaap_RangeMember_F37E3FE62E20824123BDFE22F83514FA_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_F37E3FE62E20824123BDFE22F83514FA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_5096A6DA8A3E77C7AF2BFE22F83588B5" xlink:to="loc_us-gaap_RangeMember_F37E3FE62E20824123BDFE22F83514FA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_78E15B32186D488B17D9FE22F8351091" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_F37E3FE62E20824123BDFE22F83514FA" xlink:to="loc_us-gaap_MinimumMember_78E15B32186D488B17D9FE22F8351091" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_CADE81FB02F617773540FE22F835DF9E" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_F37E3FE62E20824123BDFE22F83514FA" xlink:to="loc_us-gaap_MaximumMember_CADE81FB02F617773540FE22F835DF9E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_WeightedAverageMember" xlink:label="loc_us-gaap_WeightedAverageMember_FC00AF4F7522C4DD2FC6FE22F83592E8" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_F37E3FE62E20824123BDFE22F83514FA" xlink:to="loc_us-gaap_WeightedAverageMember_FC00AF4F7522C4DD2FC6FE22F83592E8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisAbstract" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisAbstract_CEB4B701AB2B8C36434AFE22F8354626" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_F5398FA086C08DF0015BFE22F835B585" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisAbstract_CEB4B701AB2B8C36434AFE22F8354626" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetsFairValueDisclosureAbstract" xlink:label="loc_us-gaap_AssetsFairValueDisclosureAbstract_E0B9D9B21A010C1A8823FE22F836A4C8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisAbstract_CEB4B701AB2B8C36434AFE22F8354626" xlink:to="loc_us-gaap_AssetsFairValueDisclosureAbstract_E0B9D9B21A010C1A8823FE22F836A4C8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_D1FCDF914AEB96771C27FE22F8367B01" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_E0B9D9B21A010C1A8823FE22F836A4C8" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_D1FCDF914AEB96771C27FE22F8367B01" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherShortTermInvestments" xlink:label="loc_us-gaap_OtherShortTermInvestments_CF1EA121B259EA2D05D5FE22F8365A61" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_E0B9D9B21A010C1A8823FE22F836A4C8" xlink:to="loc_us-gaap_OtherShortTermInvestments_CF1EA121B259EA2D05D5FE22F8365A61" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeAssetsAbstract" xlink:label="loc_us-gaap_DerivativeAssetsAbstract_597DD74433F50449073AFE22F8369C8E" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_E0B9D9B21A010C1A8823FE22F836A4C8" xlink:to="loc_us-gaap_DerivativeAssetsAbstract_597DD74433F50449073AFE22F8369C8E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeAssets" xlink:label="loc_us-gaap_DerivativeAssets_2BC3B426AEC3E38FF0CCFE22F83719AE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeAssetsAbstract_597DD74433F50449073AFE22F8369C8E" xlink:to="loc_us-gaap_DerivativeAssets_2BC3B426AEC3E38FF0CCFE22F83719AE" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_NuclearFuelAndDecommissioningTrustsAbstract" xlink:label="loc_aep_NuclearFuelAndDecommissioningTrustsAbstract_CCF0365D8D3A27A61277FE22F837AC48" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_E0B9D9B21A010C1A8823FE22F836A4C8" xlink:to="loc_aep_NuclearFuelAndDecommissioningTrustsAbstract_CCF0365D8D3A27A61277FE22F837AC48" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SpentNuclearFuelAndDecommissioningTrusts" xlink:label="loc_aep_SpentNuclearFuelAndDecommissioningTrusts_AD75B9AAB76D9C0E7F59FE22F837BFEF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_NuclearFuelAndDecommissioningTrustsAbstract_CCF0365D8D3A27A61277FE22F837AC48" xlink:to="loc_aep_SpentNuclearFuelAndDecommissioningTrusts_AD75B9AAB76D9C0E7F59FE22F837BFEF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetsFairValueDisclosure" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_D873184C8248D767E735FE22F8379705" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisAbstract_CEB4B701AB2B8C36434AFE22F8354626" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_D873184C8248D767E735FE22F8379705" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LiabilitiesFairValueDisclosureAbstract" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_568689F91FC6DAF30CF1FE22F8375C69" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisAbstract_CEB4B701AB2B8C36434AFE22F8354626" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_568689F91FC6DAF30CF1FE22F8375C69" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DerivativeLiabilities" xlink:label="loc_us-gaap_DerivativeLiabilities_53C08ADEA8304BA35B54FE22F837CE61" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_568689F91FC6DAF30CF1FE22F8375C69" xlink:to="loc_us-gaap_DerivativeLiabilities_53C08ADEA8304BA35B54FE22F837CE61" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_5A55B5B631ECFEFD1DCFFE22F837439B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_F5398FA086C08DF0015BFE22F835B585" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_5A55B5B631ECFEFD1DCFFE22F837439B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisWithUnobservableInputs" xlink:label="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisWithUnobservableInputs_1C13404D77249BE250D1FE22F8377675" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_5A55B5B631ECFEFD1DCFFE22F837439B" xlink:to="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisWithUnobservableInputs_1C13404D77249BE250D1FE22F8377675" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationGainLossIncludedInEarnings" xlink:label="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationGainLossIncludedInEarnings_650E719BB92662881159FE22F837757A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_5A55B5B631ECFEFD1DCFFE22F837439B" xlink:to="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationGainLossIncludedInEarnings_650E719BB92662881159FE22F837757A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisChangeInUnrealizedGainLoss" xlink:label="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisChangeInUnrealizedGainLoss_1D342F6734928AFC935BFE22F837F53B" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_5A55B5B631ECFEFD1DCFFE22F837439B" xlink:to="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisChangeInUnrealizedGainLoss_1D342F6734928AFC935BFE22F837F53B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisGainLossIncludedInOtherComprehensiveIncomeLoss" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisGainLossIncludedInOtherComprehensiveIncomeLoss_44406599F4F7093E3FF9FE22F8388E6C" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_5A55B5B631ECFEFD1DCFFE22F837439B" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisGainLossIncludedInOtherComprehensiveIncomeLoss_44406599F4F7093E3FF9FE22F8388E6C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationPurchasesSalesIssuesSettlements" xlink:label="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationPurchasesSalesIssuesSettlements_95A624495D1E51505C4BFE22F83853D7" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_5A55B5B631ECFEFD1DCFFE22F837439B" xlink:to="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationPurchasesSalesIssuesSettlements_95A624495D1E51505C4BFE22F83853D7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationTransfersIntoLevel3" xlink:label="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationTransfersIntoLevel3_B264EAE40B403CBF6FC4FE22F838A3D8" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_5A55B5B631ECFEFD1DCFFE22F837439B" xlink:to="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationTransfersIntoLevel3_B264EAE40B403CBF6FC4FE22F838A3D8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationTransfersOutOfLevel3" xlink:label="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationTransfersOutOfLevel3_540C32BCF4903CD162C4FE22F838F45F" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_5A55B5B631ECFEFD1DCFFE22F837439B" xlink:to="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationTransfersOutOfLevel3_540C32BCF4903CD162C4FE22F838F45F" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ChangesInFairValueAllocatedToRegulatedJurisdiction" xlink:label="loc_aep_ChangesInFairValueAllocatedToRegulatedJurisdiction_EF1F7E1480E447775E1DFE22F83887DB" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_5A55B5B631ECFEFD1DCFFE22F837439B" xlink:to="loc_aep_ChangesInFairValueAllocatedToRegulatedJurisdiction_EF1F7E1480E447775E1DFE22F83887DB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueInputsQuantitativeInformationAbstract" xlink:label="loc_us-gaap_FairValueInputsQuantitativeInformationAbstract_5B8DD5356D32045ECFA4FE22F838288C" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_F5398FA086C08DF0015BFE22F835B585" xlink:to="loc_us-gaap_FairValueInputsQuantitativeInformationAbstract_5B8DD5356D32045ECFA4FE22F838288C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_FairValueSignificantUnobservableInputPricePerUnit" xlink:label="loc_aep_FairValueSignificantUnobservableInputPricePerUnit_92E5526D2022EADFAF52FE22F838A522" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueInputsQuantitativeInformationAbstract_5B8DD5356D32045ECFA4FE22F838288C" xlink:to="loc_aep_FairValueSignificantUnobservableInputPricePerUnit_92E5526D2022EADFAF52FE22F838A522" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueInputsCounterpartyCreditRisk" xlink:label="loc_us-gaap_FairValueInputsCounterpartyCreditRisk_E1861F53B7AA64EF599DFE22F8389721" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueInputsQuantitativeInformationAbstract_5B8DD5356D32045ECFA4FE22F838288C" xlink:to="loc_us-gaap_FairValueInputsCounterpartyCreditRisk_E1861F53B7AA64EF599DFE22F8389721" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_FairValueMeasurements1TextualsAbstract" xlink:label="loc_aep_FairValueMeasurements1TextualsAbstract_03A4564B90543DAB8D17FE22F83822A8" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_F5398FA086C08DF0015BFE22F835B585" xlink:to="loc_aep_FairValueMeasurements1TextualsAbstract_03A4564B90543DAB8D17FE22F83822A8" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaturityOfNetFairValueOfRiskManagementContractsPriorToCashCollateralAssetsOrLiabilities" xlink:label="loc_aep_MaturityOfNetFairValueOfRiskManagementContractsPriorToCashCollateralAssetsOrLiabilities_391A8C0F2949471A2529FE22F8388E03" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_FairValueMeasurements1TextualsAbstract_03A4564B90543DAB8D17FE22F83822A8" xlink:to="loc_aep_MaturityOfNetFairValueOfRiskManagementContractsPriorToCashCollateralAssetsOrLiabilities_391A8C0F2949471A2529FE22F8388E03" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/FairValueLongTermDebtOtherTemporaryInvestmentsNuclearTrustsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_EF9578BB2A2955D4BDA3033829FC40AF" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_7105B879BD460C7C0687033829FA078B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_EF9578BB2A2955D4BDA3033829FC40AF" xlink:to="loc_us-gaap_StatementTable_7105B879BD460C7C0687033829FA078B" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_6D380218343C1DB147BC033829FA08CE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_7105B879BD460C7C0687033829FA078B" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_6D380218343C1DB147BC033829FA08CE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_2A61D479EC929C7348AF033829FA465C_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_6D380218343C1DB147BC033829FA08CE" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_2A61D479EC929C7348AF033829FA465C_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_2A61D479EC929C7348AF033829FA465C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_6D380218343C1DB147BC033829FA08CE" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_2A61D479EC929C7348AF033829FA465C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashMember" xlink:label="loc_us-gaap_CashMember_2E474C9CA36B152EA95B033829FA8766" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_2A61D479EC929C7348AF033829FA465C" xlink:to="loc_us-gaap_CashMember_2E474C9CA36B152EA95B033829FA8766" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FixedIncomeFundsMember" xlink:label="loc_us-gaap_FixedIncomeFundsMember_C93017AAA7C9D4460DA5033829FA4822" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_2A61D479EC929C7348AF033829FA465C" xlink:to="loc_us-gaap_FixedIncomeFundsMember_C93017AAA7C9D4460DA5033829FA4822" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MutualFundsFixedIncomeMember" xlink:label="loc_aep_MutualFundsFixedIncomeMember_450DB73948228EB73DD7033829FA5DDA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FixedIncomeFundsMember_C93017AAA7C9D4460DA5033829FA4822" xlink:to="loc_aep_MutualFundsFixedIncomeMember_450DB73948228EB73DD7033829FA5DDA" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_DomesticMember" xlink:label="loc_aep_DomesticMember_1D76111FA7C95E24A125033829FA9497" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_2A61D479EC929C7348AF033829FA465C" xlink:to="loc_aep_DomesticMember_1D76111FA7C95E24A125033829FA9497" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MutualFundsEquityMember" xlink:label="loc_aep_MutualFundsEquityMember_39B147672F2F5826C426033829FAE5BE" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_2A61D479EC929C7348AF033829FA465C" xlink:to="loc_aep_MutualFundsEquityMember_39B147672F2F5826C426033829FAE5BE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashAndCashEquivalentsMember" xlink:label="loc_us-gaap_CashAndCashEquivalentsMember_6238944512D5406F26D4033829FA8520" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_2A61D479EC929C7348AF033829FA465C" xlink:to="loc_us-gaap_CashAndCashEquivalentsMember_6238944512D5406F26D4033829FA8520" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_37C37D596747E10AC602033829FA3014" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_2A61D479EC929C7348AF033829FA465C" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_37C37D596747E10AC602033829FA3014" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CorporateDebtSecuritiesMember" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_F386278A26267C016C73033829FAE01C" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_2A61D479EC929C7348AF033829FA465C" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_F386278A26267C016C73033829FAE01C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StateAndLocalJurisdictionMember" xlink:label="loc_us-gaap_StateAndLocalJurisdictionMember_1B9777DE14895527577D033829FADFE5" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_2A61D479EC929C7348AF033829FA465C" xlink:to="loc_us-gaap_StateAndLocalJurisdictionMember_1B9777DE14895527577D033829FADFE5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_BD7EF4D5BED411B125B5033829FAAF2B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_7105B879BD460C7C0687033829FA078B" xlink:to="loc_dei_LegalEntityAxis_BD7EF4D5BED411B125B5033829FAAF2B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_5149C19E4F4502256E96033829FBF6FA_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_BD7EF4D5BED411B125B5033829FAAF2B" xlink:to="loc_dei_EntityDomain_5149C19E4F4502256E96033829FBF6FA_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_5149C19E4F4502256E96033829FBF6FA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_BD7EF4D5BED411B125B5033829FAAF2B" xlink:to="loc_dei_EntityDomain_5149C19E4F4502256E96033829FBF6FA" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTexasInc.Member" xlink:label="loc_aep_AEPTexasInc.Member_3D1973E9D770C3E8AFD6033829FBF94E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_5149C19E4F4502256E96033829FBF6FA" xlink:to="loc_aep_AEPTexasInc.Member_3D1973E9D770C3E8AFD6033829FBF94E" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTransmissionCoMember" xlink:label="loc_aep_AEPTransmissionCoMember_20E55EC985B4CD4BEE37033829FB506E" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_5149C19E4F4502256E96033829FBF6FA" xlink:to="loc_aep_AEPTransmissionCoMember_20E55EC985B4CD4BEE37033829FB506E" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AppalachianPowerCoMember" xlink:label="loc_aep_AppalachianPowerCoMember_3CBBB2891632D4ED3DD4033829FB9898" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_5149C19E4F4502256E96033829FBF6FA" xlink:to="loc_aep_AppalachianPowerCoMember_3CBBB2891632D4ED3DD4033829FB9898" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IndianaMichiganPowerCoMember" xlink:label="loc_aep_IndianaMichiganPowerCoMember_5EE8D700F9719F725355033829FB2EBF" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_5149C19E4F4502256E96033829FBF6FA" xlink:to="loc_aep_IndianaMichiganPowerCoMember_5EE8D700F9719F725355033829FB2EBF" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OhioPowerCoMember" xlink:label="loc_aep_OhioPowerCoMember_4C422944F012B8041195033829FB6D7E" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_5149C19E4F4502256E96033829FBF6FA" xlink:to="loc_aep_OhioPowerCoMember_4C422944F012B8041195033829FB6D7E" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_PublicServiceCoOfOklahomaMember" xlink:label="loc_aep_PublicServiceCoOfOklahomaMember_49CE6F7467481F3DC9D9033829FCE022" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_5149C19E4F4502256E96033829FBF6FA" xlink:to="loc_aep_PublicServiceCoOfOklahomaMember_49CE6F7467481F3DC9D9033829FCE022" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SouthwesternElectricPowerCoMember" xlink:label="loc_aep_SouthwesternElectricPowerCoMember_FF2C0FAA29AC6D3A4452033829FCD77C" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_5149C19E4F4502256E96033829FBF6FA" xlink:to="loc_aep_SouthwesternElectricPowerCoMember_FF2C0FAA29AC6D3A4452033829FCD77C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_TrustAssetsAxis" xlink:label="loc_aep_TrustAssetsAxis_28A29D02CB5C038884D0033829FC8B28" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_7105B879BD460C7C0687033829FA078B" xlink:to="loc_aep_TrustAssetsAxis_28A29D02CB5C038884D0033829FC8B28" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_TrustAssetsDomain" xlink:label="loc_aep_TrustAssetsDomain_55B58C0FE8A1E1FA6415033829FC5117_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_aep_TrustAssetsAxis_28A29D02CB5C038884D0033829FC8B28" xlink:to="loc_aep_TrustAssetsDomain_55B58C0FE8A1E1FA6415033829FC5117_default" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_TrustAssetsDomain" xlink:label="loc_aep_TrustAssetsDomain_55B58C0FE8A1E1FA6415033829FC5117" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_aep_TrustAssetsAxis_28A29D02CB5C038884D0033829FC8B28" xlink:to="loc_aep_TrustAssetsDomain_55B58C0FE8A1E1FA6415033829FC5117" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SpentNuclearFuelandDecommissioningTrustsMember" xlink:label="loc_aep_SpentNuclearFuelandDecommissioningTrustsMember_27B00156F133C6184DBB033829FCED1E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_TrustAssetsDomain_55B58C0FE8A1E1FA6415033829FC5117" xlink:to="loc_aep_SpentNuclearFuelandDecommissioningTrustsMember_27B00156F133C6184DBB033829FCED1E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermDebtOtherDisclosuresAbstract" xlink:label="loc_us-gaap_LongTermDebtOtherDisclosuresAbstract_737770957A4474292FD8033829FC3408" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_EF9578BB2A2955D4BDA3033829FC40AF" xlink:to="loc_us-gaap_LongTermDebtOtherDisclosuresAbstract_737770957A4474292FD8033829FC3408" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermDebt" xlink:label="loc_us-gaap_LongTermDebt_17775D8944248F2C8063033829FC1B17" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtOtherDisclosuresAbstract_737770957A4474292FD8033829FC3408" xlink:to="loc_us-gaap_LongTermDebt_17775D8944248F2C8063033829FC1B17" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermDebtFairValue" xlink:label="loc_us-gaap_LongTermDebtFairValue_A8D68BF29A781B00689E033829FDAB8E" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtOtherDisclosuresAbstract_737770957A4474292FD8033829FC3408" xlink:to="loc_us-gaap_LongTermDebtFairValue_A8D68BF29A781B00689E033829FDAB8E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShortTermInvestmentsAbstract" xlink:label="loc_us-gaap_ShortTermInvestmentsAbstract_7000BFDB0CBC8F293568033829FD29FE" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_EF9578BB2A2955D4BDA3033829FC40AF" xlink:to="loc_us-gaap_ShortTermInvestmentsAbstract_7000BFDB0CBC8F293568033829FD29FE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentOwnedAtCost" xlink:label="loc_us-gaap_InvestmentOwnedAtCost_CFC8A6582BDC3437448C033829FD2486" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermInvestmentsAbstract_7000BFDB0CBC8F293568033829FD29FE" xlink:to="loc_us-gaap_InvestmentOwnedAtCost_CFC8A6582BDC3437448C033829FD2486" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentOwnedUnrecognizedUnrealizedAppreciation" xlink:label="loc_us-gaap_InvestmentOwnedUnrecognizedUnrealizedAppreciation_885A1E641E4D621B9DB6033829FDD0EE" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermInvestmentsAbstract_7000BFDB0CBC8F293568033829FD29FE" xlink:to="loc_us-gaap_InvestmentOwnedUnrecognizedUnrealizedAppreciation_885A1E641E4D621B9DB6033829FDD0EE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentOwnedUnrecognizedUnrealizedDepreciation" xlink:label="loc_us-gaap_InvestmentOwnedUnrecognizedUnrealizedDepreciation_22FD85EA39FE3CAABEBA033829FDCB6B" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermInvestmentsAbstract_7000BFDB0CBC8F293568033829FD29FE" xlink:to="loc_us-gaap_InvestmentOwnedUnrecognizedUnrealizedDepreciation_22FD85EA39FE3CAABEBA033829FDCB6B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherShortTermInvestments" xlink:label="loc_us-gaap_OtherShortTermInvestments_B88D6DF58DE44B612B9E033829FDCE8C" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermInvestmentsAbstract_7000BFDB0CBC8F293568033829FD29FE" xlink:to="loc_us-gaap_OtherShortTermInvestments_B88D6DF58DE44B612B9E033829FDCE8C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_DebtAndEquitySecuritiesWithinOtherTemporaryInvestmentsAbstract" xlink:label="loc_aep_DebtAndEquitySecuritiesWithinOtherTemporaryInvestmentsAbstract_7203D291955E76321106033829FDF1B5" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_EF9578BB2A2955D4BDA3033829FC40AF" xlink:to="loc_aep_DebtAndEquitySecuritiesWithinOtherTemporaryInvestmentsAbstract_7203D291955E76321106033829FDF1B5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromSaleOfShortTermInvestments" xlink:label="loc_us-gaap_ProceedsFromSaleOfShortTermInvestments_0B6D20E925E34CDF1973033829FDC867" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_DebtAndEquitySecuritiesWithinOtherTemporaryInvestmentsAbstract_7203D291955E76321106033829FDF1B5" xlink:to="loc_us-gaap_ProceedsFromSaleOfShortTermInvestments_0B6D20E925E34CDF1973033829FDC867" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsToAcquireShortTermInvestments" xlink:label="loc_us-gaap_PaymentsToAcquireShortTermInvestments_411420DE713F117C27DE033829FD7689" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_DebtAndEquitySecuritiesWithinOtherTemporaryInvestmentsAbstract_7203D291955E76321106033829FDF1B5" xlink:to="loc_us-gaap_PaymentsToAcquireShortTermInvestments_411420DE713F117C27DE033829FD7689" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_GrossRealizedGainsOnInvestmentSalesOnShortTermInvestment" xlink:label="loc_aep_GrossRealizedGainsOnInvestmentSalesOnShortTermInvestment_3290253264CA114EFAC2033829FDBEDD" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_DebtAndEquitySecuritiesWithinOtherTemporaryInvestmentsAbstract_7203D291955E76321106033829FDF1B5" xlink:to="loc_aep_GrossRealizedGainsOnInvestmentSalesOnShortTermInvestment_3290253264CA114EFAC2033829FDBEDD" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_GrossRealizedLossesOnInvestmentSalesOnShortTermInvestment" xlink:label="loc_aep_GrossRealizedLossesOnInvestmentSalesOnShortTermInvestment_8E6E81BB761F1716A753033829FD7589" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_DebtAndEquitySecuritiesWithinOtherTemporaryInvestmentsAbstract_7203D291955E76321106033829FDF1B5" xlink:to="loc_aep_GrossRealizedLossesOnInvestmentSalesOnShortTermInvestment_8E6E81BB761F1716A753033829FD7589" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_NuclearTrustFundInvestmentsAbstract" xlink:label="loc_aep_NuclearTrustFundInvestmentsAbstract_E21FA28F1BF8E5AEA58503382A02DE42" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_EF9578BB2A2955D4BDA3033829FC40AF" xlink:to="loc_aep_NuclearTrustFundInvestmentsAbstract_E21FA28F1BF8E5AEA58503382A02DE42" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SpentNuclearFuelAndDecommissioningTrusts" xlink:label="loc_aep_SpentNuclearFuelAndDecommissioningTrusts_024EBDF8432979C214AD03382A02A3E0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_NuclearTrustFundInvestmentsAbstract_E21FA28F1BF8E5AEA58503382A02DE42" xlink:to="loc_aep_SpentNuclearFuelAndDecommissioningTrusts_024EBDF8432979C214AD03382A02A3E0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGains" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGains_CF7ADFFCC4A35664675603382A022161" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_NuclearTrustFundInvestmentsAbstract_E21FA28F1BF8E5AEA58503382A02DE42" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGains_CF7ADFFCC4A35664675603382A022161" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsAvailableforsaleSecurities" xlink:label="loc_us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsAvailableforsaleSecurities_59C276E2D886B783E6E703382A024A9B" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_NuclearTrustFundInvestmentsAbstract_E21FA28F1BF8E5AEA58503382A02DE42" xlink:to="loc_us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsAvailableforsaleSecurities_59C276E2D886B783E6E703382A024A9B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_UnrealizedGainOnSecurities" xlink:label="loc_us-gaap_UnrealizedGainOnSecurities_6097D60F22814F89AF7003600AB5BEFF" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_NuclearTrustFundInvestmentsAbstract_E21FA28F1BF8E5AEA58503382A02DE42" xlink:to="loc_us-gaap_UnrealizedGainOnSecurities_6097D60F22814F89AF7003600AB5BEFF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_UnrealizedLossOnSecurities" xlink:label="loc_us-gaap_UnrealizedLossOnSecurities_3E7D24C4BFD1C418746E035DD318C535" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_NuclearTrustFundInvestmentsAbstract_E21FA28F1BF8E5AEA58503382A02DE42" xlink:to="loc_us-gaap_UnrealizedLossOnSecurities_3E7D24C4BFD1C418746E035DD318C535" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SecuritiesActivityWithinDecommissioningAndSnfTrustsAbstract" xlink:label="loc_aep_SecuritiesActivityWithinDecommissioningAndSnfTrustsAbstract_B9AF78CA92D5A96AA65C03382A026CA4" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_EF9578BB2A2955D4BDA3033829FC40AF" xlink:to="loc_aep_SecuritiesActivityWithinDecommissioningAndSnfTrustsAbstract_B9AF78CA92D5A96AA65C03382A026CA4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities" xlink:label="loc_us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities_6E993D3B520A3B74EF8D03382A033B9A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_SecuritiesActivityWithinDecommissioningAndSnfTrustsAbstract_B9AF78CA92D5A96AA65C03382A026CA4" xlink:to="loc_us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities_6E993D3B520A3B74EF8D03382A033B9A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsToAcquireAvailableForSaleSecurities" xlink:label="loc_us-gaap_PaymentsToAcquireAvailableForSaleSecurities_3A43702D9734B8058C1F03382A037BF0" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_SecuritiesActivityWithinDecommissioningAndSnfTrustsAbstract_B9AF78CA92D5A96AA65C03382A026CA4" xlink:to="loc_us-gaap_PaymentsToAcquireAvailableForSaleSecurities_3A43702D9734B8058C1F03382A037BF0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AvailableForSaleSecuritiesGrossRealizedGains" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesGrossRealizedGains_D0334B08B16C6D42106203382A031FCF" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_SecuritiesActivityWithinDecommissioningAndSnfTrustsAbstract_B9AF78CA92D5A96AA65C03382A026CA4" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesGrossRealizedGains_D0334B08B16C6D42106203382A031FCF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses_1529FC1E3AF7415D767903382A03490F" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_SecuritiesActivityWithinDecommissioningAndSnfTrustsAbstract_B9AF78CA92D5A96AA65C03382A026CA4" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses_1529FC1E3AF7415D767903382A03490F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_HeldToMaturitySecuritiesDebtMaturitiesFairValueAbstract" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesFairValueAbstract_1763EC2B8D18E8553AF503382A0356C0" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_EF9578BB2A2955D4BDA3033829FC40AF" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesFairValueAbstract_1763EC2B8D18E8553AF503382A0356C0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesNextRollingTwelveMonthsFairValue" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesNextRollingTwelveMonthsFairValue_7098DD179C6BA3474E3103382A0382C4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesFairValueAbstract_1763EC2B8D18E8553AF503382A0356C0" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesNextRollingTwelveMonthsFairValue_7098DD179C6BA3474E3103382A0382C4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearTwoThroughFiveFairValue" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearTwoThroughFiveFairValue_D2CB99A71D8A6E31C5E603382A03F152" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesFairValueAbstract_1763EC2B8D18E8553AF503382A0356C0" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearTwoThroughFiveFairValue_D2CB99A71D8A6E31C5E603382A03F152" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearSixThroughTenFairValue" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearSixThroughTenFairValue_051A0E2A43DEF72ACC0503382A0389CC" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesFairValueAbstract_1763EC2B8D18E8553AF503382A0356C0" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearSixThroughTenFairValue_051A0E2A43DEF72ACC0503382A0389CC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingAfterYearTenFairValue" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingAfterYearTenFairValue_263B6B15C0D490332A3803382A048033" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesFairValueAbstract_1763EC2B8D18E8553AF503382A0356C0" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingAfterYearTenFairValue_263B6B15C0D490332A3803382A048033" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_FairValueMeasurementsTextualsAbstract" xlink:label="loc_aep_FairValueMeasurementsTextualsAbstract_9A77AFC8AA313C3216A803382A042E4B" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_EF9578BB2A2955D4BDA3033829FC40AF" xlink:to="loc_aep_FairValueMeasurementsTextualsAbstract_9A77AFC8AA313C3216A803382A042E4B" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AdjustedCostOfDebtSecurities" xlink:label="loc_aep_AdjustedCostOfDebtSecurities_E23A7F0D6F7027AEA7D103382A0458E9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_FairValueMeasurementsTextualsAbstract_9A77AFC8AA313C3216A803382A042E4B" xlink:to="loc_aep_AdjustedCostOfDebtSecurities_E23A7F0D6F7027AEA7D103382A0458E9" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AdjustedCostOfEquitySecurities" xlink:label="loc_aep_AdjustedCostOfEquitySecurities_A3474A40B11ACA86D36003382A04A0F1" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_FairValueMeasurementsTextualsAbstract_9A77AFC8AA313C3216A803382A042E4B" xlink:to="loc_aep_AdjustedCostOfEquitySecurities_A3474A40B11ACA86D36003382A04A0F1" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/FairValueMeasurements" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_5ED762A7044D88212992FD0AEC0F48C9" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_392688DEAC73AC2D39F8FD0AEC0FC49C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_5ED762A7044D88212992FD0AEC0F48C9" xlink:to="loc_us-gaap_StatementTable_392688DEAC73AC2D39F8FD0AEC0FC49C" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_639C81C51AAC9352A200FD0AEC0FD9AC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_392688DEAC73AC2D39F8FD0AEC0FC49C" xlink:to="loc_dei_LegalEntityAxis_639C81C51AAC9352A200FD0AEC0FD9AC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_4E4551519470B7C123F6FD0AEC0F0828_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_639C81C51AAC9352A200FD0AEC0FD9AC" xlink:to="loc_dei_EntityDomain_4E4551519470B7C123F6FD0AEC0F0828_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_4E4551519470B7C123F6FD0AEC0F0828" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_639C81C51AAC9352A200FD0AEC0FD9AC" xlink:to="loc_dei_EntityDomain_4E4551519470B7C123F6FD0AEC0F0828" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueDisclosuresTextBlock" xlink:label="loc_us-gaap_FairValueDisclosuresTextBlock_944A5CDBF162BA135BF4FD0AEC0F88F1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_5ED762A7044D88212992FD0AEC0F48C9" xlink:to="loc_us-gaap_FairValueDisclosuresTextBlock_944A5CDBF162BA135BF4FD0AEC0F88F1" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/FairValueMeasurementsNucInvestmentsTextualsDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.aep.com/role/FairValueMeasurementsPolicies" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_8AF62A47E3016D5C0F02FD0AEC0F42B7" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_A498956E3BE0DD2617A0FD0AEC0F8E55" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_8AF62A47E3016D5C0F02FD0AEC0F42B7" xlink:to="loc_us-gaap_StatementTable_A498956E3BE0DD2617A0FD0AEC0F8E55" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_AB0D5916E0A9AD7A2252FD0AEC0FD77A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_A498956E3BE0DD2617A0FD0AEC0F8E55" xlink:to="loc_dei_LegalEntityAxis_AB0D5916E0A9AD7A2252FD0AEC0FD77A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_B2CF75BCB0F4DEF70979FD0AEC0F9567_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_AB0D5916E0A9AD7A2252FD0AEC0FD77A" xlink:to="loc_dei_EntityDomain_B2CF75BCB0F4DEF70979FD0AEC0F9567_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_B2CF75BCB0F4DEF70979FD0AEC0F9567" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_AB0D5916E0A9AD7A2252FD0AEC0FD77A" xlink:to="loc_dei_EntityDomain_B2CF75BCB0F4DEF70979FD0AEC0F9567" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementPolicyPolicyTextBlock" xlink:label="loc_us-gaap_FairValueMeasurementPolicyPolicyTextBlock_C6894AD45B5A56C8CFD3FD0AEC0FEBFD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_8AF62A47E3016D5C0F02FD0AEC0F42B7" xlink:to="loc_us-gaap_FairValueMeasurementPolicyPolicyTextBlock_C6894AD45B5A56C8CFD3FD0AEC0FEBFD" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_BookValuesAndFairValuesOfLongTermDebtPolicyTextBlock" xlink:label="loc_aep_BookValuesAndFairValuesOfLongTermDebtPolicyTextBlock_95FE81E06AC677FC2BF6FD0AEC0F5561" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_8AF62A47E3016D5C0F02FD0AEC0F42B7" xlink:to="loc_aep_BookValuesAndFairValuesOfLongTermDebtPolicyTextBlock_95FE81E06AC677FC2BF6FD0AEC0F5561" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_TrustAssetsForDecommissioningAndSpentNuclearFuelDisposalPolicyTextBlock" xlink:label="loc_aep_TrustAssetsForDecommissioningAndSpentNuclearFuelDisposalPolicyTextBlock_A60EC4A3649D1E42117EFD0AEC0F3351" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_8AF62A47E3016D5C0F02FD0AEC0F42B7" xlink:to="loc_aep_TrustAssetsForDecommissioningAndSpentNuclearFuelDisposalPolicyTextBlock_A60EC4A3649D1E42117EFD0AEC0F3351" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisPolicyTextBlock" xlink:label="loc_aep_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisPolicyTextBlock_0EF7FB896270A903F5ADFD0AEC0F3C8F" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_8AF62A47E3016D5C0F02FD0AEC0F42B7" xlink:to="loc_aep_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisPolicyTextBlock_0EF7FB896270A903F5ADFD0AEC0F3C8F" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/FairValueMeasurementsTables" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_E9A267626652B9FB55F267EB543B49F7" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_A0EBA0AEDA08B57A123367EB543BA3D6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_E9A267626652B9FB55F267EB543B49F7" xlink:to="loc_us-gaap_StatementTable_A0EBA0AEDA08B57A123367EB543BA3D6" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_3D08809818BB837B1AA767EB543B5016" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_A0EBA0AEDA08B57A123367EB543BA3D6" xlink:to="loc_dei_LegalEntityAxis_3D08809818BB837B1AA767EB543B5016" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_CC481D3A856341A5831D67EB543B0B92_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_3D08809818BB837B1AA767EB543B5016" xlink:to="loc_dei_EntityDomain_CC481D3A856341A5831D67EB543B0B92_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_CC481D3A856341A5831D67EB543B0B92" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_3D08809818BB837B1AA767EB543B5016" xlink:to="loc_dei_EntityDomain_CC481D3A856341A5831D67EB543B0B92" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueByBalanceSheetGroupingTextBlock" xlink:label="loc_us-gaap_FairValueByBalanceSheetGroupingTextBlock_B06A9036E64DCC7C426967EB543B4481" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E9A267626652B9FB55F267EB543B49F7" xlink:to="loc_us-gaap_FairValueByBalanceSheetGroupingTextBlock_B06A9036E64DCC7C426967EB543B4481" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OtherTemporaryInvestmentsTextBlock" xlink:label="loc_aep_OtherTemporaryInvestmentsTextBlock_AAC083F1EFA3436B02A367EB543BAB8E" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E9A267626652B9FB55F267EB543B49F7" xlink:to="loc_aep_OtherTemporaryInvestmentsTextBlock_AAC083F1EFA3436B02A367EB543BAB8E" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_DebtAndEquitySecuritiesWithinOtherTemporaryInvestmentsTextBlock" xlink:label="loc_aep_DebtAndEquitySecuritiesWithinOtherTemporaryInvestmentsTextBlock_2F4AADD6AB423257CD9667EB543BC1BD" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E9A267626652B9FB55F267EB543B49F7" xlink:to="loc_aep_DebtAndEquitySecuritiesWithinOtherTemporaryInvestmentsTextBlock_2F4AADD6AB423257CD9667EB543BC1BD" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_NuclearTrustFundInvestmentsTextBlock" xlink:label="loc_aep_NuclearTrustFundInvestmentsTextBlock_91E658DF5EF11C1DC1C567EB543BBCD7" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E9A267626652B9FB55F267EB543B49F7" xlink:to="loc_aep_NuclearTrustFundInvestmentsTextBlock_91E658DF5EF11C1DC1C567EB543BBCD7" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SecuritiesActivityWithinDecommissioningAndSnfTrustsTextBlock" xlink:label="loc_aep_SecuritiesActivityWithinDecommissioningAndSnfTrustsTextBlock_23FA6630597EAAF1F11367EB543B76C7" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E9A267626652B9FB55F267EB543B49F7" xlink:to="loc_aep_SecuritiesActivityWithinDecommissioningAndSnfTrustsTextBlock_23FA6630597EAAF1F11367EB543B76C7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentsClassifiedByContractualMaturityDateTableTextBlock" xlink:label="loc_us-gaap_InvestmentsClassifiedByContractualMaturityDateTableTextBlock_6991C8943A1AF70201D267EB543BF2DB" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E9A267626652B9FB55F267EB543B49F7" xlink:to="loc_us-gaap_InvestmentsClassifiedByContractualMaturityDateTableTextBlock_6991C8943A1AF70201D267EB543BF2DB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock" xlink:label="loc_us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock_02885F1628B71C834F0467EB544BB54F" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E9A267626652B9FB55F267EB543B49F7" xlink:to="loc_us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock_02885F1628B71C834F0467EB544BB54F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationTableTextBlock" xlink:label="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationTableTextBlock_E733A8319762688308B467EB544BA0B1" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E9A267626652B9FB55F267EB543B49F7" xlink:to="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationTableTextBlock_E733A8319762688308B467EB544BA0B1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueAssetsMeasuredOnNonrecurringBasisValuationTechniquesTextBlock" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnNonrecurringBasisValuationTechniquesTextBlock_5351A054E734598776C367EB544B8E45" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E9A267626652B9FB55F267EB543B49F7" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnNonrecurringBasisValuationTechniquesTextBlock_5351A054E734598776C367EB544B8E45" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueOptionQualitativeDisclosuresRelatedToElectionTextBlock" xlink:label="loc_us-gaap_FairValueOptionQualitativeDisclosuresRelatedToElectionTextBlock_9DA192DA8B419A10D8B567EB544B9071" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E9A267626652B9FB55F267EB543B49F7" xlink:to="loc_us-gaap_FairValueOptionQualitativeDisclosuresRelatedToElectionTextBlock_9DA192DA8B419A10D8B567EB544B9071" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/FinancingActivities" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_281E6C56A39BB6EB104CFD0A3DD244BE" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_84474FC2EDED769A8CA3FD0A3DD18C35" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_281E6C56A39BB6EB104CFD0A3DD244BE" xlink:to="loc_us-gaap_StatementTable_84474FC2EDED769A8CA3FD0A3DD18C35" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_15B983B1979F3E4AF2D5FD0A3DD198D0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_84474FC2EDED769A8CA3FD0A3DD18C35" xlink:to="loc_dei_LegalEntityAxis_15B983B1979F3E4AF2D5FD0A3DD198D0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_BD374240FC9D43DC020EFD0A3DD1BE86_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_15B983B1979F3E4AF2D5FD0A3DD198D0" xlink:to="loc_dei_EntityDomain_BD374240FC9D43DC020EFD0A3DD1BE86_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_BD374240FC9D43DC020EFD0A3DD1BE86" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_15B983B1979F3E4AF2D5FD0A3DD198D0" xlink:to="loc_dei_EntityDomain_BD374240FC9D43DC020EFD0A3DD1BE86" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtDisclosureTextBlock" xlink:label="loc_us-gaap_DebtDisclosureTextBlock_69B58AF0661F3072CA44FD0A3DD2F59A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_281E6C56A39BB6EB104CFD0A3DD244BE" xlink:to="loc_us-gaap_DebtDisclosureTextBlock_69B58AF0661F3072CA44FD0A3DD2F59A" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/FinancingActivitiesDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_2EB606BD16A1B4855AB9F41542B0417B" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_D35D67C95B3ED28C6D94F41542AE9560" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_2EB606BD16A1B4855AB9F41542B0417B" xlink:to="loc_us-gaap_StatementTable_D35D67C95B3ED28C6D94F41542AE9560" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShortTermDebtTypeAxis" xlink:label="loc_us-gaap_ShortTermDebtTypeAxis_1FC66F5934782134447BF41542AE62C1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_D35D67C95B3ED28C6D94F41542AE9560" xlink:to="loc_us-gaap_ShortTermDebtTypeAxis_1FC66F5934782134447BF41542AE62C1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShortTermDebtTypeDomain" xlink:label="loc_us-gaap_ShortTermDebtTypeDomain_A95BA41B36A7DC667E32F41542AE7DCB_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ShortTermDebtTypeAxis_1FC66F5934782134447BF41542AE62C1" xlink:to="loc_us-gaap_ShortTermDebtTypeDomain_A95BA41B36A7DC667E32F41542AE7DCB_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShortTermDebtTypeDomain" xlink:label="loc_us-gaap_ShortTermDebtTypeDomain_A95BA41B36A7DC667E32F41542AE7DCB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ShortTermDebtTypeAxis_1FC66F5934782134447BF41542AE62C1" xlink:to="loc_us-gaap_ShortTermDebtTypeDomain_A95BA41B36A7DC667E32F41542AE7DCB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommercialPaperMember" xlink:label="loc_us-gaap_CommercialPaperMember_2AD4D2EAE289A22F979EF41542AE6D14" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtTypeDomain_A95BA41B36A7DC667E32F41542AE7DCB" xlink:to="loc_us-gaap_CommercialPaperMember_2AD4D2EAE289A22F979EF41542AE6D14" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LoansPayableMember" xlink:label="loc_us-gaap_LoansPayableMember_7E6F0A86E187554E800DF41542AEFC96" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtTypeDomain_A95BA41B36A7DC667E32F41542AE7DCB" xlink:to="loc_us-gaap_LoansPayableMember_7E6F0A86E187554E800DF41542AEFC96" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_D696C2FD0354B9AB618AF41542AEF5CC" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_D35D67C95B3ED28C6D94F41542AE9560" xlink:to="loc_dei_LegalEntityAxis_D696C2FD0354B9AB618AF41542AEF5CC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_0480F3DED3A0BE358626F41542AED3AF_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_D696C2FD0354B9AB618AF41542AEF5CC" xlink:to="loc_dei_EntityDomain_0480F3DED3A0BE358626F41542AED3AF_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_0480F3DED3A0BE358626F41542AED3AF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_D696C2FD0354B9AB618AF41542AEF5CC" xlink:to="loc_dei_EntityDomain_0480F3DED3A0BE358626F41542AED3AF" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTexasInc.Member" xlink:label="loc_aep_AEPTexasInc.Member_48FD075B3BC85F253FDBF41542AE0733" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_0480F3DED3A0BE358626F41542AED3AF" xlink:to="loc_aep_AEPTexasInc.Member_48FD075B3BC85F253FDBF41542AE0733" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTransmissionCoMember" xlink:label="loc_aep_AEPTransmissionCoMember_08D071631B5BE254D20AF41542AEFBFB" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_0480F3DED3A0BE358626F41542AED3AF" xlink:to="loc_aep_AEPTransmissionCoMember_08D071631B5BE254D20AF41542AEFBFB" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AppalachianPowerCoMember" xlink:label="loc_aep_AppalachianPowerCoMember_325AB81941DB4D071FD7F41542AE2EC0" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_0480F3DED3A0BE358626F41542AED3AF" xlink:to="loc_aep_AppalachianPowerCoMember_325AB81941DB4D071FD7F41542AE2EC0" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IndianaMichiganPowerCoMember" xlink:label="loc_aep_IndianaMichiganPowerCoMember_A592F3EAEA928282380FF41542AF05F6" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_0480F3DED3A0BE358626F41542AED3AF" xlink:to="loc_aep_IndianaMichiganPowerCoMember_A592F3EAEA928282380FF41542AF05F6" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OhioPowerCoMember" xlink:label="loc_aep_OhioPowerCoMember_CD32D5D96D261A04B9E1F41542AFBF53" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_0480F3DED3A0BE358626F41542AED3AF" xlink:to="loc_aep_OhioPowerCoMember_CD32D5D96D261A04B9E1F41542AFBF53" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_PublicServiceCoOfOklahomaMember" xlink:label="loc_aep_PublicServiceCoOfOklahomaMember_2B2880E643D4F9AE0F6BF41542AF8DA4" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_0480F3DED3A0BE358626F41542AED3AF" xlink:to="loc_aep_PublicServiceCoOfOklahomaMember_2B2880E643D4F9AE0F6BF41542AF8DA4" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SouthwesternElectricPowerCoMember" xlink:label="loc_aep_SouthwesternElectricPowerCoMember_C745BB1A51F8B5816AA2F41542AF907B" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_0480F3DED3A0BE358626F41542AED3AF" xlink:to="loc_aep_SouthwesternElectricPowerCoMember_C745BB1A51F8B5816AA2F41542AF907B" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_TransourceEnergyMember" xlink:label="loc_aep_TransourceEnergyMember_05C9F40578894AC6B7A6F41542AFC7BF" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_0480F3DED3A0BE358626F41542AED3AF" xlink:to="loc_aep_TransourceEnergyMember_05C9F40578894AC6B7A6F41542AFC7BF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentAxis" xlink:label="loc_us-gaap_DebtInstrumentAxis_DEF12620A5196E222DD9F41542AFAD22" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_D35D67C95B3ED28C6D94F41542AE9560" xlink:to="loc_us-gaap_DebtInstrumentAxis_DEF12620A5196E222DD9F41542AFAD22" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_775CB3BBB4E549397CFBF41542AF2931_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_DEF12620A5196E222DD9F41542AFAD22" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_775CB3BBB4E549397CFBF41542AF2931_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_775CB3BBB4E549397CFBF41542AF2931" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_DEF12620A5196E222DD9F41542AFAD22" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_775CB3BBB4E549397CFBF41542AF2931" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NotesPayableOtherPayablesMember" xlink:label="loc_us-gaap_NotesPayableOtherPayablesMember_970C16B74E5041455F54F41542AFD8A8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_775CB3BBB4E549397CFBF41542AF2931" xlink:to="loc_us-gaap_NotesPayableOtherPayablesMember_970C16B74E5041455F54F41542AFD8A8" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_NotesPayableOtherPayableTwoMember" xlink:label="loc_aep_NotesPayableOtherPayableTwoMember_A464E131D22838FE2D95F41542AF2E3B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_775CB3BBB4E549397CFBF41542AF2931" xlink:to="loc_aep_NotesPayableOtherPayableTwoMember_A464E131D22838FE2D95F41542AF2E3B" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_NotesPayableOtherPayableThreeMember" xlink:label="loc_aep_NotesPayableOtherPayableThreeMember_23FDD39139EA014E2D22F41542AF3035" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_775CB3BBB4E549397CFBF41542AF2931" xlink:to="loc_aep_NotesPayableOtherPayableThreeMember_23FDD39139EA014E2D22F41542AF3035" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_NotesPayableOtherPayableFourMember" xlink:label="loc_aep_NotesPayableOtherPayableFourMember_A1E7139D05DA74604357F41542AF534D" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_775CB3BBB4E549397CFBF41542AF2931" xlink:to="loc_aep_NotesPayableOtherPayableFourMember_A1E7139D05DA74604357F41542AF534D" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_NotesPayableOtherPayableFiveMember" xlink:label="loc_aep_NotesPayableOtherPayableFiveMember_998DD166EE00BCD4CCE2F41542AFABA0" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_775CB3BBB4E549397CFBF41542AF2931" xlink:to="loc_aep_NotesPayableOtherPayableFiveMember_998DD166EE00BCD4CCE2F41542AFABA0" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OtherLongTermDebtMember" xlink:label="loc_aep_OtherLongTermDebtMember_DB0524E25B49B8C2E9CAF41542AFD1AA" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_775CB3BBB4E549397CFBF41542AF2931" xlink:to="loc_aep_OtherLongTermDebtMember_DB0524E25B49B8C2E9CAF41542AFD1AA" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_PollutionControlBondsMember" xlink:label="loc_aep_PollutionControlBondsMember_5BF28367AE6715B348EBF4AE20933249" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_775CB3BBB4E549397CFBF41542AF2931" xlink:to="loc_aep_PollutionControlBondsMember_5BF28367AE6715B348EBF4AE20933249" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SecuritizationBondsMember" xlink:label="loc_aep_SecuritizationBondsMember_1CE3DB133575517B3380F41542B034E1" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_775CB3BBB4E549397CFBF41542AF2931" xlink:to="loc_aep_SecuritizationBondsMember_1CE3DB133575517B3380F41542B034E1" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SecuritizationBondsTwoMember" xlink:label="loc_aep_SecuritizationBondsTwoMember_173F26D66B881A572C7CF49C1D6C97E1" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_775CB3BBB4E549397CFBF41542AF2931" xlink:to="loc_aep_SecuritizationBondsTwoMember_173F26D66B881A572C7CF49C1D6C97E1" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SeniorUnsecuredNotesMember" xlink:label="loc_aep_SeniorUnsecuredNotesMember_09429E355D502F85FC31F41542B0DBD5" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_775CB3BBB4E549397CFBF41542AF2931" xlink:to="loc_aep_SeniorUnsecuredNotesMember_09429E355D502F85FC31F41542B0DBD5" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SeniorUnsecuredNotesTwoMember" xlink:label="loc_aep_SeniorUnsecuredNotesTwoMember_EE2C919770BA66A17908F41542B07F9D" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_775CB3BBB4E549397CFBF41542AF2931" xlink:to="loc_aep_SeniorUnsecuredNotesTwoMember_EE2C919770BA66A17908F41542B07F9D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_5EBED40F94277DD2FAF8F41542B07A22" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_D35D67C95B3ED28C6D94F41542AE9560" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_5EBED40F94277DD2FAF8F41542B07A22" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_66AE9DDC02074DBE0C32F41542B0CC66_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_5EBED40F94277DD2FAF8F41542B07A22" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_66AE9DDC02074DBE0C32F41542B0CC66_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_66AE9DDC02074DBE0C32F41542B0CC66" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_5EBED40F94277DD2FAF8F41542B07A22" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_66AE9DDC02074DBE0C32F41542B0CC66" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventMember" xlink:label="loc_us-gaap_SubsequentEventMember_F4A8B0A07C34919026CFF41542B082CB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_66AE9DDC02074DBE0C32F41542B0CC66" xlink:to="loc_us-gaap_SubsequentEventMember_F4A8B0A07C34919026CFF41542B082CB" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MoneyPoolParticipantbyCompanyTypeAxis" xlink:label="loc_aep_MoneyPoolParticipantbyCompanyTypeAxis_495111F21F1D42F7BF41F41542B0E0A3" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_D35D67C95B3ED28C6D94F41542AE9560" xlink:to="loc_aep_MoneyPoolParticipantbyCompanyTypeAxis_495111F21F1D42F7BF41F41542B0E0A3" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MoneyPoolParticipantbyCompanyTypeDomain" xlink:label="loc_aep_MoneyPoolParticipantbyCompanyTypeDomain_5D8D4AA1756A467CAC31F41542B0B068_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_aep_MoneyPoolParticipantbyCompanyTypeAxis_495111F21F1D42F7BF41F41542B0E0A3" xlink:to="loc_aep_MoneyPoolParticipantbyCompanyTypeDomain_5D8D4AA1756A467CAC31F41542B0B068_default" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MoneyPoolParticipantbyCompanyTypeDomain" xlink:label="loc_aep_MoneyPoolParticipantbyCompanyTypeDomain_5D8D4AA1756A467CAC31F41542B0B068" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_aep_MoneyPoolParticipantbyCompanyTypeAxis_495111F21F1D42F7BF41F41542B0E0A3" xlink:to="loc_aep_MoneyPoolParticipantbyCompanyTypeDomain_5D8D4AA1756A467CAC31F41542B0B068" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_UtilityMember" xlink:label="loc_aep_UtilityMember_3E63C6473533374000F7F41542B0F465" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_MoneyPoolParticipantbyCompanyTypeDomain_5D8D4AA1756A467CAC31F41542B0B068" xlink:to="loc_aep_UtilityMember_3E63C6473533374000F7F41542B0F465" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_NonutilityMember" xlink:label="loc_aep_NonutilityMember_6F70FC3E20335B7E85D7F41542B0525B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_MoneyPoolParticipantbyCompanyTypeDomain_5D8D4AA1756A467CAC31F41542B0B068" xlink:to="loc_aep_NonutilityMember_6F70FC3E20335B7E85D7F41542B0525B" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_DirectBorrowingMember" xlink:label="loc_aep_DirectBorrowingMember_9252E3F47BBD338861FEF41542B0DDAA" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_MoneyPoolParticipantbyCompanyTypeDomain_5D8D4AA1756A467CAC31F41542B0B068" xlink:to="loc_aep_DirectBorrowingMember_9252E3F47BBD338861FEF41542B0DDAA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermDebtAbstract" xlink:label="loc_us-gaap_LongTermDebtAbstract_5AF8386C848F3D9EB2D5F41542B1B307" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_2EB606BD16A1B4855AB9F41542B0417B" xlink:to="loc_us-gaap_LongTermDebtAbstract_5AF8386C848F3D9EB2D5F41542B1B307" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_UnsecuredDebt" xlink:label="loc_us-gaap_UnsecuredDebt_CCD5EA6A40BA14E5A4A0F41542B1C008" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtAbstract_5AF8386C848F3D9EB2D5F41542B1B307" xlink:to="loc_us-gaap_UnsecuredDebt_CCD5EA6A40BA14E5A4A0F41542B1C008" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongtermPollutionControlBondCurrentAndNoncurrent" xlink:label="loc_us-gaap_LongtermPollutionControlBondCurrentAndNoncurrent_8BE48C5BDC4722285BCBF41542B1DD9E" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtAbstract_5AF8386C848F3D9EB2D5F41542B1B307" xlink:to="loc_us-gaap_LongtermPollutionControlBondCurrentAndNoncurrent_8BE48C5BDC4722285BCBF41542B1DD9E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherNotesPayable" xlink:label="loc_us-gaap_OtherNotesPayable_C44B71BA0A465CFEDE35F41542B10A03" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtAbstract_5AF8386C848F3D9EB2D5F41542B1B307" xlink:to="loc_us-gaap_OtherNotesPayable_C44B71BA0A465CFEDE35F41542B10A03" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SecuredDebt" xlink:label="loc_us-gaap_SecuredDebt_BEAF41523AD0223B7EEAF41542B13820" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtAbstract_5AF8386C848F3D9EB2D5F41542B1B307" xlink:to="loc_us-gaap_SecuredDebt_BEAF41523AD0223B7EEAF41542B13820" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SpentNuclearFuelObligationNoncurrent" xlink:label="loc_us-gaap_SpentNuclearFuelObligationNoncurrent_7460A9355D3E824867A0F41542B18ED3" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtAbstract_5AF8386C848F3D9EB2D5F41542B1B307" xlink:to="loc_us-gaap_SpentNuclearFuelObligationNoncurrent_7460A9355D3E824867A0F41542B18ED3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherLongTermDebt" xlink:label="loc_us-gaap_OtherLongTermDebt_048CD6798B4E0553737DF41542B10B70" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtAbstract_5AF8386C848F3D9EB2D5F41542B1B307" xlink:to="loc_us-gaap_OtherLongTermDebt_048CD6798B4E0553737DF41542B10B70" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermDebt" xlink:label="loc_us-gaap_LongTermDebt_B66B298279CD939DDF37F41542B1B6FA" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtAbstract_5AF8386C848F3D9EB2D5F41542B1B307" xlink:to="loc_us-gaap_LongTermDebt_B66B298279CD939DDF37F41542B1B6FA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermDebtCurrent" xlink:label="loc_us-gaap_LongTermDebtCurrent_E1A13C0839C9B28EADA2F41542B1972F" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtAbstract_5AF8386C848F3D9EB2D5F41542B1B307" xlink:to="loc_us-gaap_LongTermDebtCurrent_E1A13C0839C9B28EADA2F41542B1972F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermDebtNoncurrent" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_6C131C2D13B19F48B87AF41542B1AA00" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtAbstract_5AF8386C848F3D9EB2D5F41542B1B307" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_6C131C2D13B19F48B87AF41542B1AA00" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_LongTermDebtAndOtherSecuritiesIssuedRetiredAndPrincipalPaymentsMadeAbstract" xlink:label="loc_aep_LongTermDebtAndOtherSecuritiesIssuedRetiredAndPrincipalPaymentsMadeAbstract_A6FDADDADB3A1DBAFC7EF41542B1F497" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_2EB606BD16A1B4855AB9F41542B0417B" xlink:to="loc_aep_LongTermDebtAndOtherSecuritiesIssuedRetiredAndPrincipalPaymentsMadeAbstract_A6FDADDADB3A1DBAFC7EF41542B1F497" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromIssuanceOfDebt" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfDebt_755763E92D840275CBADF41542B1E7AC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_LongTermDebtAndOtherSecuritiesIssuedRetiredAndPrincipalPaymentsMadeAbstract_A6FDADDADB3A1DBAFC7EF41542B1F497" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfDebt_755763E92D840275CBADF41542B1E7AC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RepaymentsOfLongTermDebt" xlink:label="loc_us-gaap_RepaymentsOfLongTermDebt_3A7C225C243CC0401718F41542B1A877" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_LongTermDebtAndOtherSecuritiesIssuedRetiredAndPrincipalPaymentsMadeAbstract_A6FDADDADB3A1DBAFC7EF41542B1F497" xlink:to="loc_us-gaap_RepaymentsOfLongTermDebt_3A7C225C243CC0401718F41542B1A877" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_F0D2E0A78F33481FEEF9F41542B1EB64" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_LongTermDebtAndOtherSecuritiesIssuedRetiredAndPrincipalPaymentsMadeAbstract_A6FDADDADB3A1DBAFC7EF41542B1F497" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_F0D2E0A78F33481FEEF9F41542B1EB64" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_DebtInstrumentInterestVariableRate" xlink:label="loc_aep_DebtInstrumentInterestVariableRate_44B2BE4724B92F8A8BDEF41542B112F6" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_LongTermDebtAndOtherSecuritiesIssuedRetiredAndPrincipalPaymentsMadeAbstract_A6FDADDADB3A1DBAFC7EF41542B1F497" xlink:to="loc_aep_DebtInstrumentInterestVariableRate_44B2BE4724B92F8A8BDEF41542B112F6" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_DebtInstrumentMaturityDate1" xlink:label="loc_aep_DebtInstrumentMaturityDate1_456E510856F1621495B8F41542B2665A" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_LongTermDebtAndOtherSecuritiesIssuedRetiredAndPrincipalPaymentsMadeAbstract_A6FDADDADB3A1DBAFC7EF41542B1F497" xlink:to="loc_aep_DebtInstrumentMaturityDate1_456E510856F1621495B8F41542B2665A" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MoneyPoolParticipantsMoneyPoolActivityAndAuthorizedBorrowingLimitsAbstract" xlink:label="loc_aep_MoneyPoolParticipantsMoneyPoolActivityAndAuthorizedBorrowingLimitsAbstract_5766307C1D12C080A711F41542B27DB9" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_2EB606BD16A1B4855AB9F41542B0417B" xlink:to="loc_aep_MoneyPoolParticipantsMoneyPoolActivityAndAuthorizedBorrowingLimitsAbstract_5766307C1D12C080A711F41542B27DB9" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaximumBorrowingsfromMoneyPool" xlink:label="loc_aep_MaximumBorrowingsfromMoneyPool_9AFB8350AB93D55C1AAFF41542B21B15" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_MoneyPoolParticipantsMoneyPoolActivityAndAuthorizedBorrowingLimitsAbstract_5766307C1D12C080A711F41542B27DB9" xlink:to="loc_aep_MaximumBorrowingsfromMoneyPool_9AFB8350AB93D55C1AAFF41542B21B15" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaximumLoanstoMoneyPool" xlink:label="loc_aep_MaximumLoanstoMoneyPool_9EE19361B519D612690CF41542B2A2AC" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_MoneyPoolParticipantsMoneyPoolActivityAndAuthorizedBorrowingLimitsAbstract_5766307C1D12C080A711F41542B27DB9" xlink:to="loc_aep_MaximumLoanstoMoneyPool_9EE19361B519D612690CF41542B2A2AC" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AverageBorrowingsfromMoneyPool" xlink:label="loc_aep_AverageBorrowingsfromMoneyPool_5A5EF268D0B37F108E17F41542B2184C" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_MoneyPoolParticipantsMoneyPoolActivityAndAuthorizedBorrowingLimitsAbstract_5766307C1D12C080A711F41542B27DB9" xlink:to="loc_aep_AverageBorrowingsfromMoneyPool_5A5EF268D0B37F108E17F41542B2184C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AverageLoanstoMoneyPool" xlink:label="loc_aep_AverageLoanstoMoneyPool_CBA9BCBE2CCDAC43A90FF41542B23E39" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_MoneyPoolParticipantsMoneyPoolActivityAndAuthorizedBorrowingLimitsAbstract_5766307C1D12C080A711F41542B27DB9" xlink:to="loc_aep_AverageLoanstoMoneyPool_CBA9BCBE2CCDAC43A90FF41542B23E39" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_BorrowingsfromParent" xlink:label="loc_aep_BorrowingsfromParent_D8A36BA338F7EC06EAEFF41542B2997C" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_MoneyPoolParticipantsMoneyPoolActivityAndAuthorizedBorrowingLimitsAbstract_5766307C1D12C080A711F41542B27DB9" xlink:to="loc_aep_BorrowingsfromParent_D8A36BA338F7EC06EAEFF41542B2997C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_LoanstoParent" xlink:label="loc_aep_LoanstoParent_F636B7911D1BB85A7B91F41542B2AC13" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_MoneyPoolParticipantsMoneyPoolActivityAndAuthorizedBorrowingLimitsAbstract_5766307C1D12C080A711F41542B27DB9" xlink:to="loc_aep_LoanstoParent_F636B7911D1BB85A7B91F41542B2AC13" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RelatedPartyTransactionDueFromToRelatedPartyCurrent" xlink:label="loc_us-gaap_RelatedPartyTransactionDueFromToRelatedPartyCurrent_14595A75D139F7E5F910F41542B273DB" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_MoneyPoolParticipantsMoneyPoolActivityAndAuthorizedBorrowingLimitsAbstract_5766307C1D12C080A711F41542B27DB9" xlink:to="loc_us-gaap_RelatedPartyTransactionDueFromToRelatedPartyCurrent_14595A75D139F7E5F910F41542B273DB" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AuthorizedShortTermBorrowingLimit" xlink:label="loc_aep_AuthorizedShortTermBorrowingLimit_48A3ACE1FE65C46FC726F41542B2E341" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_MoneyPoolParticipantsMoneyPoolActivityAndAuthorizedBorrowingLimitsAbstract_5766307C1D12C080A711F41542B27DB9" xlink:to="loc_aep_AuthorizedShortTermBorrowingLimit_48A3ACE1FE65C46FC726F41542B2E341" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaximumAndMinimumInterestRatesAbstract" xlink:label="loc_aep_MaximumAndMinimumInterestRatesAbstract_7A09DFB11D429B18753BF41542B26C70" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_2EB606BD16A1B4855AB9F41542B0417B" xlink:to="loc_aep_MaximumAndMinimumInterestRatesAbstract_7A09DFB11D429B18753BF41542B26C70" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaximumInterestRate" xlink:label="loc_aep_MaximumInterestRate_409771CCC2F35BC5E220F41542B2A194" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_MaximumAndMinimumInterestRatesAbstract_7A09DFB11D429B18753BF41542B26C70" xlink:to="loc_aep_MaximumInterestRate_409771CCC2F35BC5E220F41542B2A194" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MinimumInterestRate" xlink:label="loc_aep_MinimumInterestRate_35DFF760AF1EE32A7E47F41542B26D49" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_MaximumAndMinimumInterestRatesAbstract_7A09DFB11D429B18753BF41542B26C70" xlink:to="loc_aep_MinimumInterestRate_35DFF760AF1EE32A7E47F41542B26D49" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaximumInterestRateforFundsBorrowed" xlink:label="loc_aep_MaximumInterestRateforFundsBorrowed_B4728F47B42625D169DFF41542B2A81C" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_MaximumAndMinimumInterestRatesAbstract_7A09DFB11D429B18753BF41542B26C70" xlink:to="loc_aep_MaximumInterestRateforFundsBorrowed_B4728F47B42625D169DFF41542B2A81C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MinimumInterestRateForFundsBorrowed" xlink:label="loc_aep_MinimumInterestRateForFundsBorrowed_F573DC02AB163F36D50AF41542B2D69F" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_MaximumAndMinimumInterestRatesAbstract_7A09DFB11D429B18753BF41542B26C70" xlink:to="loc_aep_MinimumInterestRateForFundsBorrowed_F573DC02AB163F36D50AF41542B2D69F" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaximumInterestRateForFundsLoaned" xlink:label="loc_aep_MaximumInterestRateForFundsLoaned_F20CB1399A80BB1D34ADF41542B3FEEF" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_MaximumAndMinimumInterestRatesAbstract_7A09DFB11D429B18753BF41542B26C70" xlink:to="loc_aep_MaximumInterestRateForFundsLoaned_F20CB1399A80BB1D34ADF41542B3FEEF" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MinimumInterestRateforFundsLoaned" xlink:label="loc_aep_MinimumInterestRateforFundsLoaned_916A1C1C0A3B14841448F41542B316A1" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_MaximumAndMinimumInterestRatesAbstract_7A09DFB11D429B18753BF41542B26C70" xlink:to="loc_aep_MinimumInterestRateforFundsLoaned_916A1C1C0A3B14841448F41542B316A1" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AverageInterestRatesforFundsBorrowedFromandLoanedtoMoneyPoolAbstract" xlink:label="loc_aep_AverageInterestRatesforFundsBorrowedFromandLoanedtoMoneyPoolAbstract_805CA4D871F006A0C412F41542B34B5B" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_2EB606BD16A1B4855AB9F41542B0417B" xlink:to="loc_aep_AverageInterestRatesforFundsBorrowedFromandLoanedtoMoneyPoolAbstract_805CA4D871F006A0C412F41542B34B5B" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AverageInterestRateForFundsBorrowed" xlink:label="loc_aep_AverageInterestRateForFundsBorrowed_9D61B3807BE0E953DE38F41542B3B64C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_AverageInterestRatesforFundsBorrowedFromandLoanedtoMoneyPoolAbstract_805CA4D871F006A0C412F41542B34B5B" xlink:to="loc_aep_AverageInterestRateForFundsBorrowed_9D61B3807BE0E953DE38F41542B3B64C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AverageInterestRateForFundsLoaned" xlink:label="loc_aep_AverageInterestRateForFundsLoaned_0055F3E98522A2971211F41542B307C1" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_AverageInterestRatesforFundsBorrowedFromandLoanedtoMoneyPoolAbstract_805CA4D871F006A0C412F41542B34B5B" xlink:to="loc_aep_AverageInterestRateForFundsLoaned_0055F3E98522A2971211F41542B307C1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShortTermBorrowingsAbstract" xlink:label="loc_us-gaap_ShortTermBorrowingsAbstract_6B932C5FC493EB4B8B26F41542B3A9DD" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_2EB606BD16A1B4855AB9F41542B0417B" xlink:to="loc_us-gaap_ShortTermBorrowingsAbstract_6B932C5FC493EB4B8B26F41542B3A9DD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TransfersAccountedForAsSecuredBorrowingsAssociatedLiabilitiesCarryingAmount" xlink:label="loc_us-gaap_TransfersAccountedForAsSecuredBorrowingsAssociatedLiabilitiesCarryingAmount_12CC241F06D879B0A867F41542B384E0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermBorrowingsAbstract_6B932C5FC493EB4B8B26F41542B3A9DD" xlink:to="loc_us-gaap_TransfersAccountedForAsSecuredBorrowingsAssociatedLiabilitiesCarryingAmount_12CC241F06D879B0A867F41542B384E0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommercialPaper" xlink:label="loc_us-gaap_CommercialPaper_EA6035EF9A9EA6FF9A5BF41542B3BAE2" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermBorrowingsAbstract_6B932C5FC493EB4B8B26F41542B3A9DD" xlink:to="loc_us-gaap_CommercialPaper_EA6035EF9A9EA6FF9A5BF41542B3BAE2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NotesPayable" xlink:label="loc_us-gaap_NotesPayable_C1003AED6AE3B72AEA0EF41542B37833" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermBorrowingsAbstract_6B932C5FC493EB4B8B26F41542B3A9DD" xlink:to="loc_us-gaap_NotesPayable_C1003AED6AE3B72AEA0EF41542B37833" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShortTermBorrowings" xlink:label="loc_us-gaap_ShortTermBorrowings_C7F940EB02303CD17E17F41542B36607" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermBorrowingsAbstract_6B932C5FC493EB4B8B26F41542B3A9DD" xlink:to="loc_us-gaap_ShortTermBorrowings_C7F940EB02303CD17E17F41542B36607" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShortTermDebtWeightedAverageInterestRate" xlink:label="loc_us-gaap_ShortTermDebtWeightedAverageInterestRate_F052430BFC68C79B7784F41542B37E5E" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermBorrowingsAbstract_6B932C5FC493EB4B8B26F41542B3A9DD" xlink:to="loc_us-gaap_ShortTermDebtWeightedAverageInterestRate_F052430BFC68C79B7784F41542B37E5E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtWeightedAverageInterestRate" xlink:label="loc_us-gaap_DebtWeightedAverageInterestRate_3A08157AB5DFFAD5B87BF41542B34BD3" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermBorrowingsAbstract_6B932C5FC493EB4B8B26F41542B3A9DD" xlink:to="loc_us-gaap_DebtWeightedAverageInterestRate_3A08157AB5DFFAD5B87BF41542B34BD3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromSaleAndCollectionOfOtherReceivablesAbstract" xlink:label="loc_us-gaap_ProceedsFromSaleAndCollectionOfOtherReceivablesAbstract_BE765C5DA109D0D2BA88F41542B3949D" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_2EB606BD16A1B4855AB9F41542B0417B" xlink:to="loc_us-gaap_ProceedsFromSaleAndCollectionOfOtherReceivablesAbstract_BE765C5DA109D0D2BA88F41542B3949D" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_EffectiveInterestRatesOnSecuritizationOfAccountsReceivable" xlink:label="loc_aep_EffectiveInterestRatesOnSecuritizationOfAccountsReceivable_398E20CEFD7C25666D6CF41542B3C5BD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProceedsFromSaleAndCollectionOfOtherReceivablesAbstract_BE765C5DA109D0D2BA88F41542B3949D" xlink:to="loc_aep_EffectiveInterestRatesOnSecuritizationOfAccountsReceivable_398E20CEFD7C25666D6CF41542B3C5BD" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_NetUncollectibleAccountsReceivableWrittenOff" xlink:label="loc_aep_NetUncollectibleAccountsReceivableWrittenOff_0B8EC256E12561EDA857F41542B37CC2" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProceedsFromSaleAndCollectionOfOtherReceivablesAbstract_BE765C5DA109D0D2BA88F41542B3949D" xlink:to="loc_aep_NetUncollectibleAccountsReceivableWrittenOff_0B8EC256E12561EDA857F41542B37CC2" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_CustomerAccountsReceivableManagedPortfolioAbstract" xlink:label="loc_aep_CustomerAccountsReceivableManagedPortfolioAbstract_97318DA098686216DCDFF41542B37194" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_2EB606BD16A1B4855AB9F41542B0417B" xlink:to="loc_aep_CustomerAccountsReceivableManagedPortfolioAbstract_97318DA098686216DCDFF41542B37194" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AccountsReceivableRetainedInterestAndPledgedAsCollateralLessUncollectibleAccounts" xlink:label="loc_aep_AccountsReceivableRetainedInterestAndPledgedAsCollateralLessUncollectibleAccounts_BEF2538F19D7870D80B7F41542B4097E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CustomerAccountsReceivableManagedPortfolioAbstract_97318DA098686216DCDFF41542B37194" xlink:to="loc_aep_AccountsReceivableRetainedInterestAndPledgedAsCollateralLessUncollectibleAccounts_BEF2538F19D7870D80B7F41542B4097E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PrincipalAmountOutstandingOnLoansHeldForSaleOrSecuritization" xlink:label="loc_us-gaap_PrincipalAmountOutstandingOnLoansHeldForSaleOrSecuritization_F34FC77CDCD802457C7BF41542B40BE7" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CustomerAccountsReceivableManagedPortfolioAbstract_97318DA098686216DCDFF41542B37194" xlink:to="loc_us-gaap_PrincipalAmountOutstandingOnLoansHeldForSaleOrSecuritization_F34FC77CDCD802457C7BF41542B40BE7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DelinquentAmountAtEndOfPeriodOnLoansManagedAndSecuritized" xlink:label="loc_us-gaap_DelinquentAmountAtEndOfPeriodOnLoansManagedAndSecuritized_DB478F28EDB3588EF8BFF41542B4C672" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CustomerAccountsReceivableManagedPortfolioAbstract_97318DA098686216DCDFF41542B37194" xlink:to="loc_us-gaap_DelinquentAmountAtEndOfPeriodOnLoansManagedAndSecuritized_DB478F28EDB3588EF8BFF41542B4C672" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_BadDebtReservesRelatedToSecuritizedSaleOfAccountsReceivable" xlink:label="loc_aep_BadDebtReservesRelatedToSecuritizedSaleOfAccountsReceivable_505EBDA6998D88B85756F41542B43C4D" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CustomerAccountsReceivableManagedPortfolioAbstract_97318DA098686216DCDFF41542B37194" xlink:to="loc_aep_BadDebtReservesRelatedToSecuritizedSaleOfAccountsReceivable_505EBDA6998D88B85756F41542B43C4D" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_UnbilledReceivablesRelatedToSecuritizationSaleOfAccountsReceivable" xlink:label="loc_aep_UnbilledReceivablesRelatedToSecuritizationSaleOfAccountsReceivable_DBEA18B4A7B72BF76D57F41542B4532B" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CustomerAccountsReceivableManagedPortfolioAbstract_97318DA098686216DCDFF41542B37194" xlink:to="loc_aep_UnbilledReceivablesRelatedToSecuritizationSaleOfAccountsReceivable_DBEA18B4A7B72BF76D57F41542B4532B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ReceivablesHeldForSaleAbstract" xlink:label="loc_us-gaap_ReceivablesHeldForSaleAbstract_C7A5426731ADB9E21247F41542B4EAA2" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_2EB606BD16A1B4855AB9F41542B0417B" xlink:to="loc_us-gaap_ReceivablesHeldForSaleAbstract_C7A5426731ADB9E21247F41542B4EAA2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ReceivablesHeldForSaleAmount" xlink:label="loc_us-gaap_ReceivablesHeldForSaleAmount_4A82E416011636E03413F41542B469D7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReceivablesHeldForSaleAbstract_C7A5426731ADB9E21247F41542B4EAA2" xlink:to="loc_us-gaap_ReceivablesHeldForSaleAmount_4A82E416011636E03413F41542B469D7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FeesAndCommissionsAbstract" xlink:label="loc_us-gaap_FeesAndCommissionsAbstract_DE507785E78DAF470006F41542B4DB4F" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_2EB606BD16A1B4855AB9F41542B0417B" xlink:to="loc_us-gaap_FeesAndCommissionsAbstract_DE507785E78DAF470006F41542B4DB4F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DistributionAndServicingFees" xlink:label="loc_us-gaap_DistributionAndServicingFees_693452AAFA48FC5A1CC8F41542B4180C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FeesAndCommissionsAbstract_DE507785E78DAF470006F41542B4DB4F" xlink:to="loc_us-gaap_DistributionAndServicingFees_693452AAFA48FC5A1CC8F41542B4180C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromSaleAndCollectionOfReceivablesAbstract" xlink:label="loc_us-gaap_ProceedsFromSaleAndCollectionOfReceivablesAbstract_AC91902918969592274EF41542B4439C" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_2EB606BD16A1B4855AB9F41542B0417B" xlink:to="loc_us-gaap_ProceedsFromSaleAndCollectionOfReceivablesAbstract_AC91902918969592274EF41542B4439C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromSaleOfFinanceReceivables" xlink:label="loc_us-gaap_ProceedsFromSaleOfFinanceReceivables_C24C2E727BDEAA74A448F41542B40E7D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProceedsFromSaleAndCollectionOfReceivablesAbstract_AC91902918969592274EF41542B4439C" xlink:to="loc_us-gaap_ProceedsFromSaleOfFinanceReceivables_C24C2E727BDEAA74A448F41542B40E7D" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_FinancingActivitiesTextualsAbstract" xlink:label="loc_aep_FinancingActivitiesTextualsAbstract_9EE02832CB5F62032E07F41542B475DB" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_2EB606BD16A1B4855AB9F41542B0417B" xlink:to="loc_aep_FinancingActivitiesTextualsAbstract_9EE02832CB5F62032E07F41542B475DB" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_TrustFundAssetsOneTimeFeeObligationForNuclearFuelDisposition" xlink:label="loc_aep_TrustFundAssetsOneTimeFeeObligationForNuclearFuelDisposition_8100BE7B2EA94F9DD2D6F41542B461B0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_FinancingActivitiesTextualsAbstract_9EE02832CB5F62032E07F41542B475DB" xlink:to="loc_aep_TrustFundAssetsOneTimeFeeObligationForNuclearFuelDisposition_8100BE7B2EA94F9DD2D6F41542B461B0" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AuctionRateTaxExemptLongTermDebtOutstanding" xlink:label="loc_aep_AuctionRateTaxExemptLongTermDebtOutstanding_F1C656804C73AE1FD7C5F41542B53520" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_FinancingActivitiesTextualsAbstract_9EE02832CB5F62032E07F41542B475DB" xlink:to="loc_aep_AuctionRateTaxExemptLongTermDebtOutstanding_F1C656804C73AE1FD7C5F41542B53520" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SubLimitofSecuredDebt" xlink:label="loc_aep_SubLimitofSecuredDebt_9FC62522C9EB3C932362F41542B5D229" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_FinancingActivitiesTextualsAbstract_9EE02832CB5F62032E07F41542B475DB" xlink:to="loc_aep_SubLimitofSecuredDebt_9FC62522C9EB3C932362F41542B5D229" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaximumPercentageofConsolidatedTangibleNetAssets" xlink:label="loc_aep_MaximumPercentageofConsolidatedTangibleNetAssets_449B0FF77789F248D4F4F41542B500E3" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_FinancingActivitiesTextualsAbstract_9EE02832CB5F62032E07F41542B475DB" xlink:to="loc_aep_MaximumPercentageofConsolidatedTangibleNetAssets_449B0FF77789F248D4F4F41542B500E3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TangibleCapitalToTangibleAssets" xlink:label="loc_us-gaap_TangibleCapitalToTangibleAssets_AC648F88EFB10B148B28F46C772B4D0D" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_FinancingActivitiesTextualsAbstract_9EE02832CB5F62032E07F41542B475DB" xlink:to="loc_us-gaap_TangibleCapitalToTangibleAssets_AC648F88EFB10B148B28F46C772B4D0D" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaximumPercentageDebtToCapitalization" xlink:label="loc_aep_MaximumPercentageDebtToCapitalization_CB12441585844253FDEBF41542B53D0B" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_FinancingActivitiesTextualsAbstract_9EE02832CB5F62032E07F41542B475DB" xlink:to="loc_aep_MaximumPercentageDebtToCapitalization_CB12441585844253FDEBF41542B53D0B" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_TotalCommitmentFromBankConduitsToFinanceReceivables" xlink:label="loc_aep_TotalCommitmentFromBankConduitsToFinanceReceivables_427C6D0DFCE8702E1A07F41542B5D138" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_FinancingActivitiesTextualsAbstract_9EE02832CB5F62032E07F41542B475DB" xlink:to="loc_aep_TotalCommitmentFromBankConduitsToFinanceReceivables_427C6D0DFCE8702E1A07F41542B5D138" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/FinancingActivitiesTables" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_953BFB62B22F6169A8409C38F3F93203" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_2E84F2F07D7924EB2FCB9C38F3F97D5E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_953BFB62B22F6169A8409C38F3F93203" xlink:to="loc_us-gaap_StatementTable_2E84F2F07D7924EB2FCB9C38F3F97D5E" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_03175D472F36552FDC269C38F3F9CC34" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_2E84F2F07D7924EB2FCB9C38F3F97D5E" xlink:to="loc_dei_LegalEntityAxis_03175D472F36552FDC269C38F3F9CC34" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_6725A4528B284FB8F9509C38F3F9FCFA_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_03175D472F36552FDC269C38F3F9CC34" xlink:to="loc_dei_EntityDomain_6725A4528B284FB8F9509C38F3F9FCFA_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_6725A4528B284FB8F9509C38F3F9FCFA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_03175D472F36552FDC269C38F3F9CC34" xlink:to="loc_dei_EntityDomain_6725A4528B284FB8F9509C38F3F9FCFA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfDebtTableTextBlock" xlink:label="loc_us-gaap_ScheduleOfDebtTableTextBlock_58CD02B0E7133EC4148E9C38F3F931D6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_953BFB62B22F6169A8409C38F3F93203" xlink:to="loc_us-gaap_ScheduleOfDebtTableTextBlock_58CD02B0E7133EC4148E9C38F3F931D6" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_LongTermDebtAndOtherSecuritiesIssuedTextBlock" xlink:label="loc_aep_LongTermDebtAndOtherSecuritiesIssuedTextBlock_A353B48B1B5EFE0353FB9C38F3F96463" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_953BFB62B22F6169A8409C38F3F93203" xlink:to="loc_aep_LongTermDebtAndOtherSecuritiesIssuedTextBlock_A353B48B1B5EFE0353FB9C38F3F96463" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfExtinguishmentOfDebtTextBlock" xlink:label="loc_us-gaap_ScheduleOfExtinguishmentOfDebtTextBlock_BC0BED115C9100FE01199C38F3F9FF43" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_953BFB62B22F6169A8409C38F3F93203" xlink:to="loc_us-gaap_ScheduleOfExtinguishmentOfDebtTextBlock_BC0BED115C9100FE01199C38F3F9FF43" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_UtilityMoneyPoolParticipantsMoneyPoolActivityAndAuthorizedBorrowingLimitsTextBlock" xlink:label="loc_aep_UtilityMoneyPoolParticipantsMoneyPoolActivityAndAuthorizedBorrowingLimitsTextBlock_3D0367C1CFC1D3FB9AC29C38F3F9F596" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_953BFB62B22F6169A8409C38F3F93203" xlink:to="loc_aep_UtilityMoneyPoolParticipantsMoneyPoolActivityAndAuthorizedBorrowingLimitsTextBlock_3D0367C1CFC1D3FB9AC29C38F3F9F596" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_NonutilityMoneyPoolActivityTableTextBlock" xlink:label="loc_aep_NonutilityMoneyPoolActivityTableTextBlock_F771BFEE192C06E04CC69C38F3FA9949" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_953BFB62B22F6169A8409C38F3F93203" xlink:to="loc_aep_NonutilityMoneyPoolActivityTableTextBlock_F771BFEE192C06E04CC69C38F3FA9949" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_DirectBorrowingActivityTableTextBlock" xlink:label="loc_aep_DirectBorrowingActivityTableTextBlock_91F46BCD502F1CFAF7689C38F3FAB3EE" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_953BFB62B22F6169A8409C38F3F93203" xlink:to="loc_aep_DirectBorrowingActivityTableTextBlock_91F46BCD502F1CFAF7689C38F3FAB3EE" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaximumAndMinimumInterestRatesForFundsEitherBorrowedFromOrLoanedToUtilityMoneyPoolTextBlock" xlink:label="loc_aep_MaximumAndMinimumInterestRatesForFundsEitherBorrowedFromOrLoanedToUtilityMoneyPoolTextBlock_4F9B67CF079E13977AC19C38F3F9D7FC" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_953BFB62B22F6169A8409C38F3F93203" xlink:to="loc_aep_MaximumAndMinimumInterestRatesForFundsEitherBorrowedFromOrLoanedToUtilityMoneyPoolTextBlock_4F9B67CF079E13977AC19C38F3F9D7FC" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AverageInterestRatesForFundsBorrowedFromAndLoanedToUtilityMoneyPoolTextBlock" xlink:label="loc_aep_AverageInterestRatesForFundsBorrowedFromAndLoanedToUtilityMoneyPoolTextBlock_C381CE8F6299DF9769F39C38F3FA713E" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_953BFB62B22F6169A8409C38F3F93203" xlink:to="loc_aep_AverageInterestRatesForFundsBorrowedFromAndLoanedToUtilityMoneyPoolTextBlock_C381CE8F6299DF9769F39C38F3FA713E" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaximumMinimumAverageInterestRatesForFundsBorrowedFromLoanedToNonutilityMoneyPoolTextBlock" xlink:label="loc_aep_MaximumMinimumAverageInterestRatesForFundsBorrowedFromLoanedToNonutilityMoneyPoolTextBlock_5F305D7CFD1ED720E7A89C38F3FAD2E2" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_953BFB62B22F6169A8409C38F3F93203" xlink:to="loc_aep_MaximumMinimumAverageInterestRatesForFundsBorrowedFromLoanedToNonutilityMoneyPoolTextBlock_5F305D7CFD1ED720E7A89C38F3FAD2E2" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaximumMinimumandAverageInterestRatesforFundsBorrowedfromandLoanedtoAEPTableTextBlock" xlink:label="loc_aep_MaximumMinimumandAverageInterestRatesforFundsBorrowedfromandLoanedtoAEPTableTextBlock_F05DC82FADB7C208E9F79C38F3FADD81" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_953BFB62B22F6169A8409C38F3F93203" xlink:to="loc_aep_MaximumMinimumandAverageInterestRatesforFundsBorrowedfromandLoanedtoAEPTableTextBlock_F05DC82FADB7C208E9F79C38F3FADD81" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfShortTermDebtTextBlock" xlink:label="loc_us-gaap_ScheduleOfShortTermDebtTextBlock_0346C2A32B208234DDA79C38F3FAD305" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_953BFB62B22F6169A8409C38F3F93203" xlink:to="loc_us-gaap_ScheduleOfShortTermDebtTextBlock_0346C2A32B208234DDA79C38F3FAD305" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ComparativeAccountsReceivableInformationTextBlock" xlink:label="loc_aep_ComparativeAccountsReceivableInformationTextBlock_9A83F634A0ACCEB33F549C38F3FAFBEC" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_953BFB62B22F6169A8409C38F3F93203" xlink:to="loc_aep_ComparativeAccountsReceivableInformationTextBlock_9A83F634A0ACCEB33F549C38F3FAFBEC" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_CustomerAccountsReceivableManagedPortfolioTextBlock" xlink:label="loc_aep_CustomerAccountsReceivableManagedPortfolioTextBlock_1CA742FE79AF16C42F1E9C38F3FA9AAE" xlink:type="locator" />
    <link:definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_953BFB62B22F6169A8409C38F3F93203" xlink:to="loc_aep_CustomerAccountsReceivableManagedPortfolioTextBlock_1CA742FE79AF16C42F1E9C38F3FA9AAE" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AccountsReceivableAndAccruedUnbilledRevenuesTextBlock" xlink:label="loc_aep_AccountsReceivableAndAccruedUnbilledRevenuesTextBlock_91FBBAEA1F92F99298D79C38F3FA8CAD" xlink:type="locator" />
    <link:definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_953BFB62B22F6169A8409C38F3F93203" xlink:to="loc_aep_AccountsReceivableAndAccruedUnbilledRevenuesTextBlock_91FBBAEA1F92F99298D79C38F3FA8CAD" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_FeesPaidToAepCreditForCustomerAccountsReceivableSoldTextBlock" xlink:label="loc_aep_FeesPaidToAepCreditForCustomerAccountsReceivableSoldTextBlock_175D8816A4279A45C0979C38F3FAAF66" xlink:type="locator" />
    <link:definitionArc order="15" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_953BFB62B22F6169A8409C38F3F93203" xlink:to="loc_aep_FeesPaidToAepCreditForCustomerAccountsReceivableSoldTextBlock_175D8816A4279A45C0979C38F3FAAF66" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ProceedsOnSaleOfReceivablesToAepCreditTextBlock" xlink:label="loc_aep_ProceedsOnSaleOfReceivablesToAepCreditTextBlock_EEE7239EFAA017E1AB4B9C38F3FA9E9E" xlink:type="locator" />
    <link:definitionArc order="16" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_953BFB62B22F6169A8409C38F3F93203" xlink:to="loc_aep_ProceedsOnSaleOfReceivablesToAepCreditTextBlock_EEE7239EFAA017E1AB4B9C38F3FA9E9E" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/IncomeTaxes" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_CA805E36D1D80038B8F2FD0AEBBD3FB3" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_B3B43FA8C30D67CE17ECFD0AEBBD5B8E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_CA805E36D1D80038B8F2FD0AEBBD3FB3" xlink:to="loc_us-gaap_StatementTable_B3B43FA8C30D67CE17ECFD0AEBBD5B8E" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_E52E04700F1B6914F86AFD0AEBBD2345" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_B3B43FA8C30D67CE17ECFD0AEBBD5B8E" xlink:to="loc_dei_LegalEntityAxis_E52E04700F1B6914F86AFD0AEBBD2345" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_078D24BDB342E9839113FD0AEBBD3BC0_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_E52E04700F1B6914F86AFD0AEBBD2345" xlink:to="loc_dei_EntityDomain_078D24BDB342E9839113FD0AEBBD3BC0_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_078D24BDB342E9839113FD0AEBBD3BC0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_E52E04700F1B6914F86AFD0AEBBD2345" xlink:to="loc_dei_EntityDomain_078D24BDB342E9839113FD0AEBBD3BC0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeTaxDisclosureTextBlock" xlink:label="loc_us-gaap_IncomeTaxDisclosureTextBlock_EC85DA40B5D833FE4218FD0AEBBDA9A3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_CA805E36D1D80038B8F2FD0AEBBD3FB3" xlink:to="loc_us-gaap_IncomeTaxDisclosureTextBlock_EC85DA40B5D833FE4218FD0AEBBDA9A3" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/IncomeTaxesDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_FEC243C360F8D23EED3F01DEBE898C92" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_485ADB019F8CC4F942FA01DEBE89E3DC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_FEC243C360F8D23EED3F01DEBE898C92" xlink:to="loc_us-gaap_StatementTable_485ADB019F8CC4F942FA01DEBE89E3DC" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeTaxAuthorityAxis" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_E642B5351202AED9C28B01DEBE89A644" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_485ADB019F8CC4F942FA01DEBE89E3DC" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_E642B5351202AED9C28B01DEBE89A644" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeTaxAuthorityDomain" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_80291303AE7DBA46474B01DEBE89C809_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_E642B5351202AED9C28B01DEBE89A644" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_80291303AE7DBA46474B01DEBE89C809_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeTaxAuthorityDomain" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_80291303AE7DBA46474B01DEBE89C809" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_E642B5351202AED9C28B01DEBE89A644" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_80291303AE7DBA46474B01DEBE89C809" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_NetRegulatoryLiabilityforTaxReformMember" xlink:label="loc_aep_NetRegulatoryLiabilityforTaxReformMember_A5C24A4CAFBB41E5293601DEBE8905D5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_80291303AE7DBA46474B01DEBE89C809" xlink:to="loc_aep_NetRegulatoryLiabilityforTaxReformMember_A5C24A4CAFBB41E5293601DEBE8905D5" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IncrementalLiabilityforTaxReformMember" xlink:label="loc_aep_IncrementalLiabilityforTaxReformMember_DF10FA63657763C4B1DD01DEBE896849" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_80291303AE7DBA46474B01DEBE89C809" xlink:to="loc_aep_IncrementalLiabilityforTaxReformMember_DF10FA63657763C4B1DD01DEBE896849" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_PretaxExcessADITMember" xlink:label="loc_aep_PretaxExcessADITMember_8E9C5898F89B8323B88901DEBE898C03" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_80291303AE7DBA46474B01DEBE89C809" xlink:to="loc_aep_PretaxExcessADITMember_8E9C5898F89B8323B88901DEBE898C03" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_TemporaryDifferencesAssociatedwithDepreciablePropertyMember" xlink:label="loc_aep_TemporaryDifferencesAssociatedwithDepreciablePropertyMember_1577338F4D1DAE90554001DEBE89C247" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_80291303AE7DBA46474B01DEBE89C809" xlink:to="loc_aep_TemporaryDifferencesAssociatedwithDepreciablePropertyMember_1577338F4D1DAE90554001DEBE89C247" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RemainingExcessADITMember" xlink:label="loc_aep_RemainingExcessADITMember_FB57E46BE8E3B347B4AB01DEBE893D6B" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_80291303AE7DBA46474B01DEBE89C809" xlink:to="loc_aep_RemainingExcessADITMember_FB57E46BE8E3B347B4AB01DEBE893D6B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_2BDCC5026E01281376D901DEBE898D9A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_485ADB019F8CC4F942FA01DEBE89E3DC" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_2BDCC5026E01281376D901DEBE898D9A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_5400A069765BF9E3043901DEBE892895_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_2BDCC5026E01281376D901DEBE898D9A" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_5400A069765BF9E3043901DEBE892895_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_5400A069765BF9E3043901DEBE892895" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_2BDCC5026E01281376D901DEBE898D9A" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_5400A069765BF9E3043901DEBE892895" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventMember" xlink:label="loc_us-gaap_SubsequentEventMember_07156631F1267407413701DEBE89EF01" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_5400A069765BF9E3043901DEBE892895" xlink:to="loc_us-gaap_SubsequentEventMember_07156631F1267407413701DEBE89EF01" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_681F93E2F62D5341A97901DEBE89FDDA" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_485ADB019F8CC4F942FA01DEBE89E3DC" xlink:to="loc_dei_LegalEntityAxis_681F93E2F62D5341A97901DEBE89FDDA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_7424381735C6DCFDEE5201DEBE897061_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_681F93E2F62D5341A97901DEBE89FDDA" xlink:to="loc_dei_EntityDomain_7424381735C6DCFDEE5201DEBE897061_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_7424381735C6DCFDEE5201DEBE897061" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_681F93E2F62D5341A97901DEBE89FDDA" xlink:to="loc_dei_EntityDomain_7424381735C6DCFDEE5201DEBE897061" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTexasInc.Member" xlink:label="loc_aep_AEPTexasInc.Member_10C6B37112D4A2767D8301DEBE898025" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_7424381735C6DCFDEE5201DEBE897061" xlink:to="loc_aep_AEPTexasInc.Member_10C6B37112D4A2767D8301DEBE898025" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTransmissionCoMember" xlink:label="loc_aep_AEPTransmissionCoMember_3FD42142FABE6834443201DEBE894C1E" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_7424381735C6DCFDEE5201DEBE897061" xlink:to="loc_aep_AEPTransmissionCoMember_3FD42142FABE6834443201DEBE894C1E" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AppalachianPowerCoMember" xlink:label="loc_aep_AppalachianPowerCoMember_79BC504D7C3BDCCBE1D501DEBE89FA3C" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_7424381735C6DCFDEE5201DEBE897061" xlink:to="loc_aep_AppalachianPowerCoMember_79BC504D7C3BDCCBE1D501DEBE89FA3C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IndianaMichiganPowerCoMember" xlink:label="loc_aep_IndianaMichiganPowerCoMember_CA3E532C1F19D9976FD601DEBE8981E7" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_7424381735C6DCFDEE5201DEBE897061" xlink:to="loc_aep_IndianaMichiganPowerCoMember_CA3E532C1F19D9976FD601DEBE8981E7" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OhioPowerCoMember" xlink:label="loc_aep_OhioPowerCoMember_F3B5301EEF67A38F236901DEBE89EFF0" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_7424381735C6DCFDEE5201DEBE897061" xlink:to="loc_aep_OhioPowerCoMember_F3B5301EEF67A38F236901DEBE89EFF0" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_PublicServiceCoOfOklahomaMember" xlink:label="loc_aep_PublicServiceCoOfOklahomaMember_E8709E79E2D7B5D8220101DEBE894F5A" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_7424381735C6DCFDEE5201DEBE897061" xlink:to="loc_aep_PublicServiceCoOfOklahomaMember_E8709E79E2D7B5D8220101DEBE894F5A" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SouthwesternElectricPowerCoMember" xlink:label="loc_aep_SouthwesternElectricPowerCoMember_4E6F2313C6046F14A16401DEBE8905D7" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_7424381735C6DCFDEE5201DEBE897061" xlink:to="loc_aep_SouthwesternElectricPowerCoMember_4E6F2313C6046F14A16401DEBE8905D7" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_TaxReformTotalRevenueAxis" xlink:label="loc_aep_TaxReformTotalRevenueAxis_5B70DC36DF4D118424F601DEBE893B3C" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_485ADB019F8CC4F942FA01DEBE89E3DC" xlink:to="loc_aep_TaxReformTotalRevenueAxis_5B70DC36DF4D118424F601DEBE893B3C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_TaxReformTotalRevenueDomain" xlink:label="loc_aep_TaxReformTotalRevenueDomain_0C650D7B771C28829BD201DEBE8995D7_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_aep_TaxReformTotalRevenueAxis_5B70DC36DF4D118424F601DEBE893B3C" xlink:to="loc_aep_TaxReformTotalRevenueDomain_0C650D7B771C28829BD201DEBE8995D7_default" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_TaxReformTotalRevenueDomain" xlink:label="loc_aep_TaxReformTotalRevenueDomain_0C650D7B771C28829BD201DEBE8995D7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_aep_TaxReformTotalRevenueAxis_5B70DC36DF4D118424F601DEBE893B3C" xlink:to="loc_aep_TaxReformTotalRevenueDomain_0C650D7B771C28829BD201DEBE8995D7" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ReductioninCorporateFederalIncomeTaxRateMember" xlink:label="loc_aep_ReductioninCorporateFederalIncomeTaxRateMember_41CDB2B6D705CC77BEC201DEBE8917BA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_TaxReformTotalRevenueDomain_0C650D7B771C28829BD201DEBE8995D7" xlink:to="loc_aep_ReductioninCorporateFederalIncomeTaxRateMember_41CDB2B6D705CC77BEC201DEBE8917BA" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ExcessADITMember" xlink:label="loc_aep_ExcessADITMember_AE44C09F6F3528B96E5501DEBE8966F3" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_TaxReformTotalRevenueDomain_0C650D7B771C28829BD201DEBE8995D7" xlink:to="loc_aep_ExcessADITMember_AE44C09F6F3528B96E5501DEBE8966F3" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ExcessAccumulatedDeferredIncomeTaxes" xlink:label="loc_aep_ExcessAccumulatedDeferredIncomeTaxes_DFE0DE7C876649623A6C01DEBE891F65" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_FEC243C360F8D23EED3F01DEBE898C92" xlink:to="loc_aep_ExcessAccumulatedDeferredIncomeTaxes_DFE0DE7C876649623A6C01DEBE891F65" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IncreaseDecreaseinTotalRevenue" xlink:label="loc_aep_IncreaseDecreaseinTotalRevenue_5683B3EB48748AACCCDD01DEBE89CF06" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_FEC243C360F8D23EED3F01DEBE898C92" xlink:to="loc_aep_IncreaseDecreaseinTotalRevenue_5683B3EB48748AACCCDD01DEBE89CF06" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_E49DD02FCEBEED98670D01DEBE89B03F" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_FEC243C360F8D23EED3F01DEBE898C92" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_E49DD02FCEBEED98670D01DEBE89B03F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncreaseDecreaseInOtherCurrentLiabilities" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherCurrentLiabilities_251CFC6D95F3954340C701DEBE89E5EC" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_FEC243C360F8D23EED3F01DEBE898C92" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherCurrentLiabilities_251CFC6D95F3954340C701DEBE89E5EC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncreaseDecreaseInOtherNoncurrentLiabilities" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherNoncurrentLiabilities_9281D51297D83B15B85E01DEBE89B31C" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_FEC243C360F8D23EED3F01DEBE898C92" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherNoncurrentLiabilities_9281D51297D83B15B85E01DEBE89B31C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EffectiveIncomeTaxRateContinuingOperations" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_FB39F1C787C104B117C601DEBE894C1E" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_FEC243C360F8D23EED3F01DEBE898C92" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_FB39F1C787C104B117C601DEBE894C1E" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_KentuckyMaximumGraduatedCorporateTaxRate" xlink:label="loc_aep_KentuckyMaximumGraduatedCorporateTaxRate_53804ACFC008A4118B3A01DEBE897799" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_FEC243C360F8D23EED3F01DEBE898C92" xlink:to="loc_aep_KentuckyMaximumGraduatedCorporateTaxRate_53804ACFC008A4118B3A01DEBE897799" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_KentuckySingleCorporateTaxRate" xlink:label="loc_aep_KentuckySingleCorporateTaxRate_3CE43DABCE9060636C9501DEBE893FF0" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_FEC243C360F8D23EED3F01DEBE898C92" xlink:to="loc_aep_KentuckySingleCorporateTaxRate_3CE43DABCE9060636C9501DEBE893FF0" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/IncomeTaxesTables" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_AF0E11F79D340448C36D01DEF032C851" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_A7874027D9F6574D057001DEF0322B8A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_AF0E11F79D340448C36D01DEF032C851" xlink:to="loc_us-gaap_StatementTable_A7874027D9F6574D057001DEF0322B8A" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_F93508C3DC51F22336DB01DEF032B23F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_A7874027D9F6574D057001DEF0322B8A" xlink:to="loc_dei_LegalEntityAxis_F93508C3DC51F22336DB01DEF032B23F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_6F8CE47B684C8642143501DEF032C8CA_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_F93508C3DC51F22336DB01DEF032B23F" xlink:to="loc_dei_EntityDomain_6F8CE47B684C8642143501DEF032C8CA_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_6F8CE47B684C8642143501DEF032C8CA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_F93508C3DC51F22336DB01DEF032B23F" xlink:to="loc_dei_EntityDomain_6F8CE47B684C8642143501DEF032C8CA" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_EstimatedProvisionsforRevenueRefundRelatedtoReductioninCorporateFederalIncomeTaxRateTableTextBlock" xlink:label="loc_aep_EstimatedProvisionsforRevenueRefundRelatedtoReductioninCorporateFederalIncomeTaxRateTableTextBlock_63CA0B50576898B2F37901DEF0328399" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_AF0E11F79D340448C36D01DEF032C851" xlink:to="loc_aep_EstimatedProvisionsforRevenueRefundRelatedtoReductioninCorporateFederalIncomeTaxRateTableTextBlock_63CA0B50576898B2F37901DEF0328399" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_EstimatedProvisionsforRevenueRefundOffsettingAmortizationofExcessADITTableTextBlock" xlink:label="loc_aep_EstimatedProvisionsforRevenueRefundOffsettingAmortizationofExcessADITTableTextBlock_5679282A22D9B55774BA01DEF03241CC" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_AF0E11F79D340448C36D01DEF032C851" xlink:to="loc_aep_EstimatedProvisionsforRevenueRefundOffsettingAmortizationofExcessADITTableTextBlock_5679282A22D9B55774BA01DEF03241CC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfEffectiveIncomeTaxRateReconciliationTableTextBlock" xlink:label="loc_us-gaap_ScheduleOfEffectiveIncomeTaxRateReconciliationTableTextBlock_E9350D4CA92EE54FFB6001DEF03234D8" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_AF0E11F79D340448C36D01DEF032C851" xlink:to="loc_us-gaap_ScheduleOfEffectiveIncomeTaxRateReconciliationTableTextBlock_E9350D4CA92EE54FFB6001DEF03234D8" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/NewAccountingPronouncements" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_681E7AB6E14FCA7A9535FD0AECB9C78E" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_3D62CAA5D86BDAE7E96BFD0AECB8C01F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_681E7AB6E14FCA7A9535FD0AECB9C78E" xlink:to="loc_us-gaap_StatementTable_3D62CAA5D86BDAE7E96BFD0AECB8C01F" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_1F4D917BFC46EEC6B6A0FD0AECB842A5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_3D62CAA5D86BDAE7E96BFD0AECB8C01F" xlink:to="loc_dei_LegalEntityAxis_1F4D917BFC46EEC6B6A0FD0AECB842A5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_36212D2AE9AFFDBFA3DAFD0AECB87D17_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_1F4D917BFC46EEC6B6A0FD0AECB842A5" xlink:to="loc_dei_EntityDomain_36212D2AE9AFFDBFA3DAFD0AECB87D17_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_36212D2AE9AFFDBFA3DAFD0AECB87D17" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_1F4D917BFC46EEC6B6A0FD0AECB842A5" xlink:to="loc_dei_EntityDomain_36212D2AE9AFFDBFA3DAFD0AECB87D17" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfNewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock" xlink:label="loc_us-gaap_ScheduleOfNewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock_B84680BEC4DF956DE015FD0AECB9D0F9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_681E7AB6E14FCA7A9535FD0AECB9C78E" xlink:to="loc_us-gaap_ScheduleOfNewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock_B84680BEC4DF956DE015FD0AECB9D0F9" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/RateMatters" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_E21E35944B39193AF774F7E8C1361CEA" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_C384C6BF1CB4928E1341F7E8C126A9E6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_E21E35944B39193AF774F7E8C1361CEA" xlink:to="loc_us-gaap_StatementTable_C384C6BF1CB4928E1341F7E8C126A9E6" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_AB9CB0D74F813DDE0275F7E8C136A9F0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_C384C6BF1CB4928E1341F7E8C126A9E6" xlink:to="loc_dei_LegalEntityAxis_AB9CB0D74F813DDE0275F7E8C136A9F0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_091551E1F71D7C58D537F7E8C136E918_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_AB9CB0D74F813DDE0275F7E8C136A9F0" xlink:to="loc_dei_EntityDomain_091551E1F71D7C58D537F7E8C136E918_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_091551E1F71D7C58D537F7E8C136E918" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_AB9CB0D74F813DDE0275F7E8C136A9F0" xlink:to="loc_dei_EntityDomain_091551E1F71D7C58D537F7E8C136E918" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PublicUtilitiesDisclosureTextBlock" xlink:label="loc_us-gaap_PublicUtilitiesDisclosureTextBlock_C2AEB3FF87265FC37906F7E8C136AE9A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E21E35944B39193AF774F7E8C1361CEA" xlink:to="loc_us-gaap_PublicUtilitiesDisclosureTextBlock_C2AEB3FF87265FC37906F7E8C136AE9A" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/RateMattersEastCompaniesDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PublicUtilitiesGeneralDisclosuresLineItems" xlink:label="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PublicUtilitiesGeneralDisclosuresTable" xlink:label="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_881D582EB36BCA9ED7AEFD411B12A671" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_881D582EB36BCA9ED7AEFD411B12A671" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_D7C65D4D57C6FE45B0C7FD411B123F6C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_881D582EB36BCA9ED7AEFD411B12A671" xlink:to="loc_us-gaap_RangeAxis_D7C65D4D57C6FE45B0C7FD411B123F6C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_4FE2544FFC4642D15468FD411B13A125_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_D7C65D4D57C6FE45B0C7FD411B123F6C" xlink:to="loc_us-gaap_RangeMember_4FE2544FFC4642D15468FD411B13A125_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_4FE2544FFC4642D15468FD411B13A125" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_D7C65D4D57C6FE45B0C7FD411B123F6C" xlink:to="loc_us-gaap_RangeMember_4FE2544FFC4642D15468FD411B13A125" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_3FC2C93962D98B90DB55FD411B132528" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_4FE2544FFC4642D15468FD411B13A125" xlink:to="loc_us-gaap_MinimumMember_3FC2C93962D98B90DB55FD411B132528" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_A42A89AE5AC1A0168D15FD411B13C615" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_4FE2544FFC4642D15468FD411B13A125" xlink:to="loc_us-gaap_MaximumMember_A42A89AE5AC1A0168D15FD411B13C615" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_AD2490B0C8EBA074B8B3FD411B1351CA" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_881D582EB36BCA9ED7AEFD411B12A671" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_AD2490B0C8EBA074B8B3FD411B1351CA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_0A5A92A0268515B6473FFD411B137301_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_AD2490B0C8EBA074B8B3FD411B1351CA" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_0A5A92A0268515B6473FFD411B137301_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_0A5A92A0268515B6473FFD411B137301" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_AD2490B0C8EBA074B8B3FD411B1351CA" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_0A5A92A0268515B6473FFD411B137301" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventMember" xlink:label="loc_us-gaap_SubsequentEventMember_E513CDB6A9F5FFF9206BFD411B13ECA3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_0A5A92A0268515B6473FFD411B137301" xlink:to="loc_us-gaap_SubsequentEventMember_E513CDB6A9F5FFF9206BFD411B13ECA3" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_NoncurrentRegulatoryAssetsAxis" xlink:label="loc_aep_NoncurrentRegulatoryAssetsAxis_97BB84028CE82992034EFD411B13D813" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_881D582EB36BCA9ED7AEFD411B12A671" xlink:to="loc_aep_NoncurrentRegulatoryAssetsAxis_97BB84028CE82992034EFD411B13D813" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RegulatoryAssetsDomain" xlink:label="loc_aep_RegulatoryAssetsDomain_149252C29195B0BFF150FD411B13DA3C_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_aep_NoncurrentRegulatoryAssetsAxis_97BB84028CE82992034EFD411B13D813" xlink:to="loc_aep_RegulatoryAssetsDomain_149252C29195B0BFF150FD411B13DA3C_default" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RegulatoryAssetsDomain" xlink:label="loc_aep_RegulatoryAssetsDomain_149252C29195B0BFF150FD411B13DA3C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_aep_NoncurrentRegulatoryAssetsAxis_97BB84028CE82992034EFD411B13D813" xlink:to="loc_aep_RegulatoryAssetsDomain_149252C29195B0BFF150FD411B13DA3C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StormCostsMember" xlink:label="loc_us-gaap_StormCostsMember_345BCB09B03E4ED1080BFD411B13C2CE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_RegulatoryAssetsDomain_149252C29195B0BFF150FD411B13DA3C" xlink:to="loc_us-gaap_StormCostsMember_345BCB09B03E4ED1080BFD411B13C2CE" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_BaseRateAxis" xlink:label="loc_aep_BaseRateAxis_F02AA27FC32E26DC2D19FD411B13FA7E" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_881D582EB36BCA9ED7AEFD411B12A671" xlink:to="loc_aep_BaseRateAxis_F02AA27FC32E26DC2D19FD411B13FA7E" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_BaseRateDomain" xlink:label="loc_aep_BaseRateDomain_A281C8F07A6F08719B5FFD411B13855D_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_aep_BaseRateAxis_F02AA27FC32E26DC2D19FD411B13FA7E" xlink:to="loc_aep_BaseRateDomain_A281C8F07A6F08719B5FFD411B13855D_default" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_BaseRateDomain" xlink:label="loc_aep_BaseRateDomain_A281C8F07A6F08719B5FFD411B13855D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_aep_BaseRateAxis_F02AA27FC32E26DC2D19FD411B13FA7E" xlink:to="loc_aep_BaseRateDomain_A281C8F07A6F08719B5FFD411B13855D" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_VirginiaLegislationAffectingBiennialReviewsMember" xlink:label="loc_aep_VirginiaLegislationAffectingBiennialReviewsMember_A77C732A737C1874AAE5FD411B13D9C4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_BaseRateDomain_A281C8F07A6F08719B5FFD411B13855D" xlink:to="loc_aep_VirginiaLegislationAffectingBiennialReviewsMember_A77C732A737C1874AAE5FD411B13D9C4" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_A2017IndianaBaseRateCaseMember" xlink:label="loc_aep_A2017IndianaBaseRateCaseMember_17843E6F1BD6EC640B11FD411B1419F3" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_BaseRateDomain_A281C8F07A6F08719B5FFD411B13855D" xlink:to="loc_aep_A2017IndianaBaseRateCaseMember_17843E6F1BD6EC640B11FD411B1419F3" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_A2017MichiganBaseRateCaseMember" xlink:label="loc_aep_A2017MichiganBaseRateCaseMember_3161FB2C6384681C74EAFD411B14DDE2" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_BaseRateDomain_A281C8F07A6F08719B5FFD411B13855D" xlink:to="loc_aep_A2017MichiganBaseRateCaseMember_3161FB2C6384681C74EAFD411B14DDE2" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RockportPlantUnit2SelectiveCatalyticReductionMember" xlink:label="loc_aep_RockportPlantUnit2SelectiveCatalyticReductionMember_FA3A43C4E542D31250B3FD411B14A1C4" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_BaseRateDomain_A281C8F07A6F08719B5FFD411B13855D" xlink:to="loc_aep_RockportPlantUnit2SelectiveCatalyticReductionMember_FA3A43C4E542D31250B3FD411B14A1C4" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_A2017KentuckyBaseRateCaseMember" xlink:label="loc_aep_A2017KentuckyBaseRateCaseMember_A777384F8D9698C53B4EFD411B14B704" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_BaseRateDomain_A281C8F07A6F08719B5FFD411B13855D" xlink:to="loc_aep_A2017KentuckyBaseRateCaseMember_A777384F8D9698C53B4EFD411B14B704" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OhioElectricSecurityPlanFilingMember" xlink:label="loc_aep_OhioElectricSecurityPlanFilingMember_939EBACEA07AC4F13FDFFD411B14AB6E" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_BaseRateDomain_A281C8F07A6F08719B5FFD411B13855D" xlink:to="loc_aep_OhioElectricSecurityPlanFilingMember_939EBACEA07AC4F13FDFFD411B14AB6E" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_A2016SEETFilingMember" xlink:label="loc_aep_A2016SEETFilingMember_B7D0AF5896AF3C581AF8FD411B140092" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_BaseRateDomain_A281C8F07A6F08719B5FFD411B13855D" xlink:to="loc_aep_A2016SEETFilingMember_B7D0AF5896AF3C581AF8FD411B140092" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_FERCTransmissionComplaintMember" xlink:label="loc_aep_FERCTransmissionComplaintMember_76E071130339D83B28D2FD411B144DB2" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_BaseRateDomain_A281C8F07A6F08719B5FFD411B13855D" xlink:to="loc_aep_FERCTransmissionComplaintMember_76E071130339D83B28D2FD411B144DB2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_021DD21BB60AAAA8E1A0FD411B1493A5" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_881D582EB36BCA9ED7AEFD411B12A671" xlink:to="loc_dei_LegalEntityAxis_021DD21BB60AAAA8E1A0FD411B1493A5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_02809AE554E9D10A4320FD411B142B74_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_021DD21BB60AAAA8E1A0FD411B1493A5" xlink:to="loc_dei_EntityDomain_02809AE554E9D10A4320FD411B142B74_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_02809AE554E9D10A4320FD411B142B74" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_021DD21BB60AAAA8E1A0FD411B1493A5" xlink:to="loc_dei_EntityDomain_02809AE554E9D10A4320FD411B142B74" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTransmissionCoMember" xlink:label="loc_aep_AEPTransmissionCoMember_0361EDF270C84137EBF6FD411B144658" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_02809AE554E9D10A4320FD411B142B74" xlink:to="loc_aep_AEPTransmissionCoMember_0361EDF270C84137EBF6FD411B144658" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AppalachianPowerCoMember" xlink:label="loc_aep_AppalachianPowerCoMember_960C57EA7470FA2BFA0BFD411B145B62" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_02809AE554E9D10A4320FD411B142B74" xlink:to="loc_aep_AppalachianPowerCoMember_960C57EA7470FA2BFA0BFD411B145B62" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IndianaMichiganPowerCoMember" xlink:label="loc_aep_IndianaMichiganPowerCoMember_9A96C6C600B86844FA58FD411B143DA2" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_02809AE554E9D10A4320FD411B142B74" xlink:to="loc_aep_IndianaMichiganPowerCoMember_9A96C6C600B86844FA58FD411B143DA2" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OhioPowerCoMember" xlink:label="loc_aep_OhioPowerCoMember_274153A1F08F7D4B0447FD411B146A35" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_02809AE554E9D10A4320FD411B142B74" xlink:to="loc_aep_OhioPowerCoMember_274153A1F08F7D4B0447FD411B146A35" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_D7EB30123CC8AFE76251FD411B15B11E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_D7EB30123CC8AFE76251FD411B15B11E" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_FuelExpensesNottobeRecovered" xlink:label="loc_aep_FuelExpensesNottobeRecovered_E3402A40FA402317805FFD411B151647" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_FuelExpensesNottobeRecovered_E3402A40FA402317805FFD411B151647" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ReductioninAnnualBaseRates" xlink:label="loc_aep_ReductioninAnnualBaseRates_B8C48BC1D20E48AC20B3FD411B15366E" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_ReductioninAnnualBaseRates_B8C48BC1D20E48AC20B3FD411B15366E" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_EnergyEfficiencyProgramsToBeRequestedFromTheVirginiaSCCThroughJuly2028dollars" xlink:label="loc_aep_EnergyEfficiencyProgramsToBeRequestedFromTheVirginiaSCCThroughJuly2028dollars_CC3C5A01E2A204B6BA9EFD411B15CF39" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_EnergyEfficiencyProgramsToBeRequestedFromTheVirginiaSCCThroughJuly2028dollars_CC3C5A01E2A204B6BA9EFD411B15CF39" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_EnergyEfficiencyProgramsToBeRequestedFromTheVirginiaSCCThroughJuly2028MWs" xlink:label="loc_aep_EnergyEfficiencyProgramsToBeRequestedFromTheVirginiaSCCThroughJuly2028MWs_D002F35F18481E64C32FFD411B1560E6" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_EnergyEfficiencyProgramsToBeRequestedFromTheVirginiaSCCThroughJuly2028MWs_D002F35F18481E64C32FFD411B1560E6" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RequestedAnnualIncrease" xlink:label="loc_aep_RequestedAnnualIncrease_A614DCE9CA01FDEB7C5CFD411B15EDA6" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_RequestedAnnualIncrease_A614DCE9CA01FDEB7C5CFD411B15EDA6" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RequestedReturnOnEquity" xlink:label="loc_aep_RequestedReturnOnEquity_9B35EB3F569166E0556BFD411B1506C8" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_RequestedReturnOnEquity_9B35EB3F569166E0556BFD411B1506C8" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AmountOfAnnualReductionToCustomerBillsThroughCreditAdjustmentRider" xlink:label="loc_aep_AmountOfAnnualReductionToCustomerBillsThroughCreditAdjustmentRider_F4AB3DF2CD95B9A05A1DFD411B154B2A" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_AmountOfAnnualReductionToCustomerBillsThroughCreditAdjustmentRider_F4AB3DF2CD95B9A05A1DFD411B154B2A" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AmountOfIncreasedDepreciationExpenseRequested" xlink:label="loc_aep_AmountOfIncreasedDepreciationExpenseRequested_F20E4260D16EF6F60360FD411B15B462" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_AmountOfIncreasedDepreciationExpenseRequested_F20E4260D16EF6F60360FD411B15B462" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AmountofIncreaseRelatedtoAmortizationofRegulatoryAssets" xlink:label="loc_aep_AmountofIncreaseRelatedtoAmortizationofRegulatoryAssets_4D83664C724827982B83FD411B15379C" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_AmountofIncreaseRelatedtoAmortizationofRegulatoryAssets_4D83664C724827982B83FD411B15379C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IntervenorRecommendedAnnualIncrease" xlink:label="loc_aep_IntervenorRecommendedAnnualIncrease_9B28030DEC26E128210DFD411B159E6D" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_IntervenorRecommendedAnnualIncrease_9B28030DEC26E128210DFD411B159E6D" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IntervenorRecommendedReturnOnCommonEquityRange" xlink:label="loc_aep_IntervenorRecommendedReturnOnCommonEquityRange_920C604B65BA37D5A406FD411B15FAA4" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_IntervenorRecommendedReturnOnCommonEquityRange_920C604B65BA37D5A406FD411B15FAA4" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AdjustedAnnualIncreaseRequestduetoTaxReform" xlink:label="loc_aep_AdjustedAnnualIncreaseRequestduetoTaxReform_0CDB0D53DD05FB387323FD411B154443" xlink:type="locator" />
    <link:definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_AdjustedAnnualIncreaseRequestduetoTaxReform_0CDB0D53DD05FB387323FD411B154443" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SetlledAnnualIncrease" xlink:label="loc_aep_SetlledAnnualIncrease_F528ABE4CD9032AB2E07FD411B152030" xlink:type="locator" />
    <link:definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_SetlledAnnualIncrease_F528ABE4CD9032AB2E07FD411B152030" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SettledReturnonCommonEquity" xlink:label="loc_aep_SettledReturnonCommonEquity_248D3B6EA0356FD39F04FD411B1533CE" xlink:type="locator" />
    <link:definitionArc order="15" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_SettledReturnonCommonEquity_248D3B6EA0356FD39F04FD411B1533CE" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OriginalSharingofOffSystemSalesMargins" xlink:label="loc_aep_OriginalSharingofOffSystemSalesMargins_B64BAF06D900467B0A5DFD411B151DE1" xlink:type="locator" />
    <link:definitionArc order="16" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_OriginalSharingofOffSystemSalesMargins_B64BAF06D900467B0A5DFD411B151DE1" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SettledSharingofOffSystemSalesMargins" xlink:label="loc_aep_SettledSharingofOffSystemSalesMargins_79034518E92DA6205EEBFD411B16F8FD" xlink:type="locator" />
    <link:definitionArc order="17" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_SettledSharingofOffSystemSalesMargins_79034518E92DA6205EEBFD411B16F8FD" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RefundforImpactofTaxReform" xlink:label="loc_aep_RefundforImpactofTaxReform_2CCC5E6CD83FF084E77DFD411B1664DF" xlink:type="locator" />
    <link:definitionArc order="18" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_RefundforImpactofTaxReform_2CCC5E6CD83FF084E77DFD411B1664DF" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ALJRecommendedAnnualIncrease" xlink:label="loc_aep_ALJRecommendedAnnualIncrease_E1BFFCF1085C0CE4E278FD411B164EA5" xlink:type="locator" />
    <link:definitionArc order="19" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_ALJRecommendedAnnualIncrease_E1BFFCF1085C0CE4E278FD411B164EA5" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_CostofNewEntryValue" xlink:label="loc_aep_CostofNewEntryValue_247C4E2BC2B37D5334AAFD411B164283" xlink:type="locator" />
    <link:definitionArc order="20" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_CostofNewEntryValue_247C4E2BC2B37D5334AAFD411B164283" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ALJRecommendedReturnonCommonEquity" xlink:label="loc_aep_ALJRecommendedReturnonCommonEquity_2BB02F2440BFBD4F5AF8FD411B16A17F" xlink:type="locator" />
    <link:definitionArc order="21" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_ALJRecommendedReturnonCommonEquity_2BB02F2440BFBD4F5AF8FD411B16A17F" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ReducedCapacityChargePretaxLoss" xlink:label="loc_aep_ReducedCapacityChargePretaxLoss_C3C5C0127D5B7FD07407FD411B161EB6" xlink:type="locator" />
    <link:definitionArc order="22" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_ReducedCapacityChargePretaxLoss_C3C5C0127D5B7FD07407FD411B161EB6" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AlternateSupplierCap" xlink:label="loc_aep_AlternateSupplierCap_67806D6AF69DE93A5643FD411B16571C" xlink:type="locator" />
    <link:definitionArc order="23" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_AlternateSupplierCap_67806D6AF69DE93A5643FD411B16571C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ApprovedAnnualRevenueIncrease" xlink:label="loc_aep_ApprovedAnnualRevenueIncrease_91E84818AAFB2B7BE414FD411B16DD84" xlink:type="locator" />
    <link:definitionArc order="24" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_ApprovedAnnualRevenueIncrease_91E84818AAFB2B7BE414FD411B16DD84" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ApprovedReturnonCommonEquity" xlink:label="loc_aep_ApprovedReturnonCommonEquity_D931C16462181D0BBA90FD411B167B14" xlink:type="locator" />
    <link:definitionArc order="25" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_ApprovedReturnonCommonEquity_D931C16462181D0BBA90FD411B167B14" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ProjectedCapitalCosts" xlink:label="loc_aep_ProjectedCapitalCosts_4BE1378851373F4A019BFD411B16503B" xlink:type="locator" />
    <link:definitionArc order="26" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_ProjectedCapitalCosts_4BE1378851373F4A019BFD411B16503B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConstructionInProgressGross" xlink:label="loc_us-gaap_ConstructionInProgressGross_3469AAA6E4B8414D3735FD411B16CB5C" xlink:type="locator" />
    <link:definitionArc order="27" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_us-gaap_ConstructionInProgressGross_3469AAA6E4B8414D3735FD411B16CB5C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ApprovedCapitalCosts" xlink:label="loc_aep_ApprovedCapitalCosts_FB20542DF2FFABBA7BD4FD411B16A1F5" xlink:type="locator" />
    <link:definitionArc order="28" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_ApprovedCapitalCosts_FB20542DF2FFABBA7BD4FD411B16A1F5" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_KPSCOrderAnnualRevenueIncrease" xlink:label="loc_aep_KPSCOrderAnnualRevenueIncrease_8760403B435E8B603B17FD411B1642CF" xlink:type="locator" />
    <link:definitionArc order="29" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_KPSCOrderAnnualRevenueIncrease_8760403B435E8B603B17FD411B1642CF" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_KPSCOrderReturnonCommonEquity" xlink:label="loc_aep_KPSCOrderReturnonCommonEquity_DB19E93F4608E3A4F3EFFD411B1638B5" xlink:type="locator" />
    <link:definitionArc order="30" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_KPSCOrderReturnonCommonEquity_DB19E93F4608E3A4F3EFFD411B1638B5" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_KPSCOrderAnnualRevenueReductionduetoTaxReform" xlink:label="loc_aep_KPSCOrderAnnualRevenueReductionduetoTaxReform_3248F580C87926A5CDF1FD411B175EA9" xlink:type="locator" />
    <link:definitionArc order="31" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_KPSCOrderAnnualRevenueReductionduetoTaxReform_3248F580C87926A5CDF1FD411B175EA9" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_KPSCOrderDeferralofRockportPlantUnitPowerAgreementExpenses" xlink:label="loc_aep_KPSCOrderDeferralofRockportPlantUnitPowerAgreementExpenses_16DAADCF9F66A1DDE0B7FD411B17523E" xlink:type="locator" />
    <link:definitionArc order="32" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_KPSCOrderDeferralofRockportPlantUnitPowerAgreementExpenses_16DAADCF9F66A1DDE0B7FD411B17523E" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RecoveryReturnofcertainPJMOATTExpensesAboveBelowCorrespondingLevelRecoveredinRates" xlink:label="loc_aep_RecoveryReturnofcertainPJMOATTExpensesAboveBelowCorrespondingLevelRecoveredinRates_9F383B0DFFE9C22F34FCFD411B17C96F" xlink:type="locator" />
    <link:definitionArc order="33" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_RecoveryReturnofcertainPJMOATTExpensesAboveBelowCorrespondingLevelRecoveredinRates_9F383B0DFFE9C22F34FCFD411B17C96F" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_KPCoRequestforAdditionalRevenueIncrease" xlink:label="loc_aep_KPCoRequestforAdditionalRevenueIncrease_C0A91BA6F5403F48447BFD411B17E71C" xlink:type="locator" />
    <link:definitionArc order="34" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_KPCoRequestforAdditionalRevenueIncrease_C0A91BA6F5403F48447BFD411B17E71C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_PUCOApprovedReducedCustomerCredits" xlink:label="loc_aep_PUCOApprovedReducedCustomerCredits_3BA0C56A809EFA56EC01FD411B1714F4" xlink:type="locator" />
    <link:definitionArc order="35" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_PUCOApprovedReducedCustomerCredits_3BA0C56A809EFA56EC01FD411B1714F4" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SolarEnergyProjectsToBeDevelopedAndImplementedBy2021AsProposedInStipulationAgreement" xlink:label="loc_aep_SolarEnergyProjectsToBeDevelopedAndImplementedBy2021AsProposedInStipulationAgreement_82D17FD722FA5FA76145FD411B178817" xlink:type="locator" />
    <link:definitionArc order="36" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_SolarEnergyProjectsToBeDevelopedAndImplementedBy2021AsProposedInStipulationAgreement_82D17FD722FA5FA76145FD411B178817" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_WindEnergyProjectsToBeDevelopedAndImplementedBy2021AsProposedInStipulationAgreement" xlink:label="loc_aep_WindEnergyProjectsToBeDevelopedAndImplementedBy2021AsProposedInStipulationAgreement_CA0948E2F352BF22405AFD411B17DC73" xlink:type="locator" />
    <link:definitionArc order="37" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_WindEnergyProjectsToBeDevelopedAndImplementedBy2021AsProposedInStipulationAgreement_CA0948E2F352BF22405AFD411B17DC73" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_PercentageofOutputtobeReceivedfromSolarandWindProjectsasProposedinStipulationAgreement" xlink:label="loc_aep_PercentageofOutputtobeReceivedfromSolarandWindProjectsasProposedinStipulationAgreement_675C7C529B1D11A2828EFD411B17EDC4" xlink:type="locator" />
    <link:definitionArc order="38" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_PercentageofOutputtobeReceivedfromSolarandWindProjectsasProposedinStipulationAgreement_675C7C529B1D11A2828EFD411B17EDC4" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaximumOwnershipPercentageofSolarandWindProjectsasProposedinStipulationAgreement" xlink:label="loc_aep_MaximumOwnershipPercentageofSolarandWindProjectsasProposedinStipulationAgreement_4783E2B145C357DB6FCBFD411B17697E" xlink:type="locator" />
    <link:definitionArc order="39" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_MaximumOwnershipPercentageofSolarandWindProjectsasProposedinStipulationAgreement_4783E2B145C357DB6FCBFD411B17697E" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ReturnonCommonEquityProposedintheAmendedESPFiling" xlink:label="loc_aep_ReturnonCommonEquityProposedintheAmendedESPFiling_FBB59086FC43D103FBD7FD411B177D7D" xlink:type="locator" />
    <link:definitionArc order="40" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_ReturnonCommonEquityProposedintheAmendedESPFiling_FBB59086FC43D103FBD7FD411B177D7D" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ReturnonCommonEquityFiledinthePendingStipulationAgreement" xlink:label="loc_aep_ReturnonCommonEquityFiledinthePendingStipulationAgreement_2728E8F7702822D35840FD411B17DF03" xlink:type="locator" />
    <link:definitionArc order="41" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_ReturnonCommonEquityFiledinthePendingStipulationAgreement_2728E8F7702822D35840FD411B17DF03" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RateCapsRelatedtotheDistributionInvestmentRiderRange" xlink:label="loc_aep_RateCapsRelatedtotheDistributionInvestmentRiderRange_51534E51825F8523C8D2FD411B17BF8A" xlink:type="locator" />
    <link:definitionArc order="42" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_RateCapsRelatedtotheDistributionInvestmentRiderRange_51534E51825F8523C8D2FD411B17BF8A" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ProvisionforRefund" xlink:label="loc_aep_ProvisionforRefund_62D0DCF11BD70AA556C2FD411B170751" xlink:type="locator" />
    <link:definitionArc order="43" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_ProvisionforRefund_62D0DCF11BD70AA556C2FD411B170751" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IntervenorRecommendedRefundtoCustomers" xlink:label="loc_aep_IntervenorRecommendedRefundtoCustomers_44F78C07810FA11F53A8FD411B1792A0" xlink:type="locator" />
    <link:definitionArc order="44" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_IntervenorRecommendedRefundtoCustomers_44F78C07810FA11F53A8FD411B1792A0" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ReturnOnCommonEquityPerSettlementAgreement" xlink:label="loc_aep_ReturnOnCommonEquityPerSettlementAgreement_C24E9A618F1425AA7CB4FD411B170707" xlink:type="locator" />
    <link:definitionArc order="45" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_ReturnOnCommonEquityPerSettlementAgreement_C24E9A618F1425AA7CB4FD411B170707" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ReturnonCommonEquityInclusiveofRTOPerSettlementAgreement" xlink:label="loc_aep_ReturnonCommonEquityInclusiveofRTOPerSettlementAgreement_D71A42D0974ACB0D1EADFD411B18368E" xlink:type="locator" />
    <link:definitionArc order="46" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_ReturnonCommonEquityInclusiveofRTOPerSettlementAgreement_D71A42D0974ACB0D1EADFD411B18368E" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RTOIncentiveAdderPerSettlementAgreement" xlink:label="loc_aep_RTOIncentiveAdderPerSettlementAgreement_882ECFBC0C5C1BC2289AFD411B18820E" xlink:type="locator" />
    <link:definitionArc order="47" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_RTOIncentiveAdderPerSettlementAgreement_882ECFBC0C5C1BC2289AFD411B18820E" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OneTimeRefundtoCustomersPerSettlementAgreement" xlink:label="loc_aep_OneTimeRefundtoCustomersPerSettlementAgreement_18FFEE2B72AC94B94AE9FD411B187D92" xlink:type="locator" />
    <link:definitionArc order="48" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_OneTimeRefundtoCustomersPerSettlementAgreement_18FFEE2B72AC94B94AE9FD411B187D92" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IncreasedCaponEquityPortionoftheCapitalStructurePerSettlementAgreement" xlink:label="loc_aep_IncreasedCaponEquityPortionoftheCapitalStructurePerSettlementAgreement_28822AF5A27A69A64BACFD411B18E039" xlink:type="locator" />
    <link:definitionArc order="49" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_IncreasedCaponEquityPortionoftheCapitalStructurePerSettlementAgreement_28822AF5A27A69A64BACFD411B18E039" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OriginalCaponEquityPortionoftheCapitalStructurePriortoSettlementAgreement" xlink:label="loc_aep_OriginalCaponEquityPortionoftheCapitalStructurePriortoSettlementAgreement_E27F3AAC9F6BF291B99EFD411B1876CE" xlink:type="locator" />
    <link:definitionArc order="50" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_OriginalCaponEquityPortionoftheCapitalStructurePriortoSettlementAgreement_E27F3AAC9F6BF291B99EFD411B1876CE" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SecondIntervenorRecommendedReturnonCommonEquity" xlink:label="loc_aep_SecondIntervenorRecommendedReturnonCommonEquity_8B16777DDCC4A5C8A089FD411B18C91E" xlink:type="locator" />
    <link:definitionArc order="51" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_SecondIntervenorRecommendedReturnonCommonEquity_8B16777DDCC4A5C8A089FD411B18C91E" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SecondIntervenorRecommendedOneTimeRefundtoCustomers" xlink:label="loc_aep_SecondIntervenorRecommendedOneTimeRefundtoCustomers_8C7D2A67A0CF75709C3EFD411B18007F" xlink:type="locator" />
    <link:definitionArc order="52" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_SecondIntervenorRecommendedOneTimeRefundtoCustomers_8C7D2A67A0CF75709C3EFD411B18007F" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_FERCTrialStaffRecommendedReturnonCommonEquity" xlink:label="loc_aep_FERCTrialStaffRecommendedReturnonCommonEquity_BFB934DA84B387A377F5FD411B184E7D" xlink:type="locator" />
    <link:definitionArc order="53" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_FERCTrialStaffRecommendedReturnonCommonEquity_BFB934DA84B387A377F5FD411B184E7D" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_FERCTrialStaffRecommendedOneTimeRefundtoCustomers" xlink:label="loc_aep_FERCTrialStaffRecommendedOneTimeRefundtoCustomers_4F704A070691DFD6198AFD411B18B2E0" xlink:type="locator" />
    <link:definitionArc order="54" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_D6DFEFEE5B0D9D7F8D9BFD411B145071" xlink:to="loc_aep_FERCTrialStaffRecommendedOneTimeRefundtoCustomers_4F704A070691DFD6198AFD411B18B2E0" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/RateMattersRegulatoryAssetsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PublicUtilitiesGeneralDisclosuresLineItems" xlink:label="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PublicUtilitiesGeneralDisclosuresTable" xlink:label="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_22E7072E99FE70458EDA01C1257BEA73" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_22E7072E99FE70458EDA01C1257BEA73" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="aep-20180331.xsd#aep_NoncurrentRegulatoryAssetsAxis" xlink:label="loc_aep_NoncurrentRegulatoryAssetsAxis_629F5488A681712F26DC01C1257B07B2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_22E7072E99FE70458EDA01C1257BEA73" xlink:to="loc_aep_NoncurrentRegulatoryAssetsAxis_629F5488A681712F26DC01C1257B07B2" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RegulatoryAssetsDomain" xlink:label="loc_aep_RegulatoryAssetsDomain_57530C3268C857F4F58A01C1257BE17C_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_aep_NoncurrentRegulatoryAssetsAxis_629F5488A681712F26DC01C1257B07B2" xlink:to="loc_aep_RegulatoryAssetsDomain_57530C3268C857F4F58A01C1257BE17C_default" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RegulatoryAssetsDomain" xlink:label="loc_aep_RegulatoryAssetsDomain_57530C3268C857F4F58A01C1257BE17C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_aep_NoncurrentRegulatoryAssetsAxis_629F5488A681712F26DC01C1257B07B2" xlink:to="loc_aep_RegulatoryAssetsDomain_57530C3268C857F4F58A01C1257BE17C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AssetRetirementObligationArkansasLouisianaMember" xlink:label="loc_aep_AssetRetirementObligationArkansasLouisianaMember_3D7426C7DA50885C90F901C1257B3EF5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_RegulatoryAssetsDomain_57530C3268C857F4F58A01C1257BE17C" xlink:to="loc_aep_AssetRetirementObligationArkansasLouisianaMember_3D7426C7DA50885C90F901C1257B3EF5" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_CookPlantTurbineMember" xlink:label="loc_aep_CookPlantTurbineMember_D4626C227F2CED3AEF4E01C1257B20BE" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_RegulatoryAssetsDomain_57530C3268C857F4F58A01C1257BE17C" xlink:to="loc_aep_CookPlantTurbineMember_D4626C227F2CED3AEF4E01C1257B20BE" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_CookPlantUprateProjectMember" xlink:label="loc_aep_CookPlantUprateProjectMember_932BEF34B3866F85CFFA01C1257B1A1E" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_RegulatoryAssetsDomain_57530C3268C857F4F58A01C1257BE17C" xlink:to="loc_aep_CookPlantUprateProjectMember_932BEF34B3866F85CFFA01C1257B1A1E" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MichiganDeferredCookPlantLifeCycleManagementProjectCostsMember" xlink:label="loc_aep_MichiganDeferredCookPlantLifeCycleManagementProjectCostsMember_A30DA573D3F480110EF101C1257B6D2C" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_RegulatoryAssetsDomain_57530C3268C857F4F58A01C1257BE17C" xlink:to="loc_aep_MichiganDeferredCookPlantLifeCycleManagementProjectCostsMember_A30DA573D3F480110EF101C1257B6D2C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OtherRegulatoryAssetsPendingFinalRegulatoryApprovalMember" xlink:label="loc_aep_OtherRegulatoryAssetsPendingFinalRegulatoryApprovalMember_6232FAE6D62B59BE868A01C1257B9E32" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_RegulatoryAssetsDomain_57530C3268C857F4F58A01C1257BE17C" xlink:to="loc_aep_OtherRegulatoryAssetsPendingFinalRegulatoryApprovalMember_6232FAE6D62B59BE868A01C1257B9E32" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AssetRetirementObligationRelatedtoRetiredPlantsMember" xlink:label="loc_aep_AssetRetirementObligationRelatedtoRetiredPlantsMember_C568BAB6CF6F6250F2E001C1257B79A6" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_RegulatoryAssetsDomain_57530C3268C857F4F58A01C1257BE17C" xlink:to="loc_aep_AssetRetirementObligationRelatedtoRetiredPlantsMember_C568BAB6CF6F6250F2E001C1257B79A6" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaterialsandSuppliesRelatedtoRetiredPlantsMember" xlink:label="loc_aep_MaterialsandSuppliesRelatedtoRetiredPlantsMember_5CEC1C3C2B9F16B5F36601C1257B61A5" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_RegulatoryAssetsDomain_57530C3268C857F4F58A01C1257BE17C" xlink:to="loc_aep_MaterialsandSuppliesRelatedtoRetiredPlantsMember_5CEC1C3C2B9F16B5F36601C1257B61A5" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_PlantRetirementCostsUnrecoveredPlantMember" xlink:label="loc_aep_PlantRetirementCostsUnrecoveredPlantMember_B665FD64B0ED4145991001C1257BD824" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_RegulatoryAssetsDomain_57530C3268C857F4F58A01C1257BE17C" xlink:to="loc_aep_PlantRetirementCostsUnrecoveredPlantMember_B665FD64B0ED4145991001C1257BD824" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RateCaseExpenseTexasMember" xlink:label="loc_aep_RateCaseExpenseTexasMember_F909BDFE6D13554E7D0101C1257B763B" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_RegulatoryAssetsDomain_57530C3268C857F4F58A01C1257BE17C" xlink:to="loc_aep_RateCaseExpenseTexasMember_F909BDFE6D13554E7D0101C1257B763B" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RateCaseExpenseMember" xlink:label="loc_aep_RateCaseExpenseMember_6E6ECCB62D9282524F7701C1257B17CF" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_RegulatoryAssetsDomain_57530C3268C857F4F58A01C1257BE17C" xlink:to="loc_aep_RateCaseExpenseMember_6E6ECCB62D9282524F7701C1257B17CF" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RockportPlantDrySorbentInjectionSystemIndianaMember" xlink:label="loc_aep_RockportPlantDrySorbentInjectionSystemIndianaMember_DDDD1A6E7C959F285E0301C1257BFE4F" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_RegulatoryAssetsDomain_57530C3268C857F4F58A01C1257BE17C" xlink:to="loc_aep_RockportPlantDrySorbentInjectionSystemIndianaMember_DDDD1A6E7C959F285E0301C1257BFE4F" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ShipeRoadTransmissionProjectMember" xlink:label="loc_aep_ShipeRoadTransmissionProjectMember_71E3377A309A22D23FE701C1257B8CB8" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_RegulatoryAssetsDomain_57530C3268C857F4F58A01C1257BE17C" xlink:to="loc_aep_ShipeRoadTransmissionProjectMember_71E3377A309A22D23FE701C1257B8CB8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StormCostsMember" xlink:label="loc_us-gaap_StormCostsMember_64D479E7747650C9396A01C1257B6A27" xlink:type="locator" />
    <link:definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_RegulatoryAssetsDomain_57530C3268C857F4F58A01C1257BE17C" xlink:to="loc_us-gaap_StormCostsMember_64D479E7747650C9396A01C1257B6A27" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_StormCostsHurricaneHarveyMember" xlink:label="loc_aep_StormCostsHurricaneHarveyMember_7B60F56311DE5285B2BE01C1257B4539" xlink:type="locator" />
    <link:definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_RegulatoryAssetsDomain_57530C3268C857F4F58A01C1257BE17C" xlink:to="loc_aep_StormCostsHurricaneHarveyMember_7B60F56311DE5285B2BE01C1257B4539" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RegulatoryAssetReturnDisclosureAxis" xlink:label="loc_aep_RegulatoryAssetReturnDisclosureAxis_0C74A40FAE989D1CC5FD01C1257B99A7" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_22E7072E99FE70458EDA01C1257BEA73" xlink:to="loc_aep_RegulatoryAssetReturnDisclosureAxis_0C74A40FAE989D1CC5FD01C1257B99A7" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RegulatoryAssetsReturnDisclosureDomain" xlink:label="loc_aep_RegulatoryAssetsReturnDisclosureDomain_18F0B0DBB9BE3A36476901C1257B4E8F_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_aep_RegulatoryAssetReturnDisclosureAxis_0C74A40FAE989D1CC5FD01C1257B99A7" xlink:to="loc_aep_RegulatoryAssetsReturnDisclosureDomain_18F0B0DBB9BE3A36476901C1257B4E8F_default" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RegulatoryAssetsReturnDisclosureDomain" xlink:label="loc_aep_RegulatoryAssetsReturnDisclosureDomain_18F0B0DBB9BE3A36476901C1257B4E8F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_aep_RegulatoryAssetReturnDisclosureAxis_0C74A40FAE989D1CC5FD01C1257B99A7" xlink:to="loc_aep_RegulatoryAssetsReturnDisclosureDomain_18F0B0DBB9BE3A36476901C1257B4E8F" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RegulatoryAssetsCurrentlyEarningReturnMember" xlink:label="loc_aep_RegulatoryAssetsCurrentlyEarningReturnMember_C8D3B3FA331EE106F74301C1257B7E4C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_RegulatoryAssetsReturnDisclosureDomain_18F0B0DBB9BE3A36476901C1257B4E8F" xlink:to="loc_aep_RegulatoryAssetsCurrentlyEarningReturnMember_C8D3B3FA331EE106F74301C1257B7E4C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RegulatoryAssetsCurrentlyNotEarningReturnMember" xlink:label="loc_aep_RegulatoryAssetsCurrentlyNotEarningReturnMember_5D9957813D75C6B4946701C1257B0250" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_RegulatoryAssetsReturnDisclosureDomain_18F0B0DBB9BE3A36476901C1257B4E8F" xlink:to="loc_aep_RegulatoryAssetsCurrentlyNotEarningReturnMember_5D9957813D75C6B4946701C1257B0250" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RegulatedStatusAxis" xlink:label="loc_aep_RegulatedStatusAxis_F2B13FF63D3B371EE58B01C1257B5A36" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_22E7072E99FE70458EDA01C1257BEA73" xlink:to="loc_aep_RegulatedStatusAxis_F2B13FF63D3B371EE58B01C1257B5A36" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RegulatedStatusDomain" xlink:label="loc_aep_RegulatedStatusDomain_59DC5B8713D124994EB501C1257B79DF_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_aep_RegulatedStatusAxis_F2B13FF63D3B371EE58B01C1257B5A36" xlink:to="loc_aep_RegulatedStatusDomain_59DC5B8713D124994EB501C1257B79DF_default" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RegulatedStatusDomain" xlink:label="loc_aep_RegulatedStatusDomain_59DC5B8713D124994EB501C1257B79DF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_aep_RegulatedStatusAxis_F2B13FF63D3B371EE58B01C1257B5A36" xlink:to="loc_aep_RegulatedStatusDomain_59DC5B8713D124994EB501C1257B79DF" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RegulatoryAssetsPendingFinalRegulatoryApprovalMember" xlink:label="loc_aep_RegulatoryAssetsPendingFinalRegulatoryApprovalMember_807D04ACCF5FC658410E01C1257B1510" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_RegulatedStatusDomain_59DC5B8713D124994EB501C1257B79DF" xlink:to="loc_aep_RegulatoryAssetsPendingFinalRegulatoryApprovalMember_807D04ACCF5FC658410E01C1257B1510" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_D45CE1A7A9A58DB913D701C1257B357E" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_22E7072E99FE70458EDA01C1257BEA73" xlink:to="loc_dei_LegalEntityAxis_D45CE1A7A9A58DB913D701C1257B357E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_3D3BB1733C5189D57FC501C1257B9A68_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_D45CE1A7A9A58DB913D701C1257B357E" xlink:to="loc_dei_EntityDomain_3D3BB1733C5189D57FC501C1257B9A68_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_3D3BB1733C5189D57FC501C1257B9A68" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_D45CE1A7A9A58DB913D701C1257B357E" xlink:to="loc_dei_EntityDomain_3D3BB1733C5189D57FC501C1257B9A68" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTexasInc.Member" xlink:label="loc_aep_AEPTexasInc.Member_1B4082F9BB094752CE0401C1257B2BD1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_3D3BB1733C5189D57FC501C1257B9A68" xlink:to="loc_aep_AEPTexasInc.Member_1B4082F9BB094752CE0401C1257B2BD1" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTransmissionCoMember" xlink:label="loc_aep_AEPTransmissionCoMember_4E3B19123EDE8A5DC27A01C1257B783F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_3D3BB1733C5189D57FC501C1257B9A68" xlink:to="loc_aep_AEPTransmissionCoMember_4E3B19123EDE8A5DC27A01C1257B783F" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AppalachianPowerCoMember" xlink:label="loc_aep_AppalachianPowerCoMember_C1285C721C8E2F51586501C1257BB51F" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_3D3BB1733C5189D57FC501C1257B9A68" xlink:to="loc_aep_AppalachianPowerCoMember_C1285C721C8E2F51586501C1257BB51F" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IndianaMichiganPowerCoMember" xlink:label="loc_aep_IndianaMichiganPowerCoMember_575D7028306E2DA99A7701C1257BDB46" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_3D3BB1733C5189D57FC501C1257B9A68" xlink:to="loc_aep_IndianaMichiganPowerCoMember_575D7028306E2DA99A7701C1257BDB46" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OhioPowerCoMember" xlink:label="loc_aep_OhioPowerCoMember_55553116E6346A5D942901C1257BE4BE" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_3D3BB1733C5189D57FC501C1257B9A68" xlink:to="loc_aep_OhioPowerCoMember_55553116E6346A5D942901C1257BE4BE" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_PublicServiceCoOfOklahomaMember" xlink:label="loc_aep_PublicServiceCoOfOklahomaMember_A8023D0ED309ABF19A5601C1257B47E4" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_3D3BB1733C5189D57FC501C1257B9A68" xlink:to="loc_aep_PublicServiceCoOfOklahomaMember_A8023D0ED309ABF19A5601C1257B47E4" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SouthwesternElectricPowerCoMember" xlink:label="loc_aep_SouthwesternElectricPowerCoMember_D16726ACB857084CE08C01C1257B2C8D" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_3D3BB1733C5189D57FC501C1257B9A68" xlink:to="loc_aep_SouthwesternElectricPowerCoMember_D16726ACB857084CE08C01C1257B2C8D" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTexasCumulativeRevenuesSubjecttoReview" xlink:label="loc_aep_AEPTexasCumulativeRevenuesSubjecttoReview_C3473BA3459AC4C5BB1701C1257B6CD3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_AEPTexasCumulativeRevenuesSubjecttoReview_C3473BA3459AC4C5BB1701C1257B6CD3" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ProposedReductioninTransmissionRatesDuetoTaxReform" xlink:label="loc_aep_ProposedReductioninTransmissionRatesDuetoTaxReform_E1BB2F267E89D3C5099E01C1257B4976" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_ProposedReductioninTransmissionRatesDuetoTaxReform_E1BB2F267E89D3C5099E01C1257B4976" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ProposedNetIncreaseinDCRF" xlink:label="loc_aep_ProposedNetIncreaseinDCRF_C13627EC2553A63F0E4D01C1257BC913" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_ProposedNetIncreaseinDCRF_C13627EC2553A63F0E4D01C1257BC913" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ProposedIncreaseinDCRFDuetoCapitalInvestments" xlink:label="loc_aep_ProposedIncreaseinDCRFDuetoCapitalInvestments_3F416F263A2E3D5DDACE01C1257B5833" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_ProposedIncreaseinDCRFDuetoCapitalInvestments_3F416F263A2E3D5DDACE01C1257B5833" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ProposedReductioninDCRFDuetoTaxReform" xlink:label="loc_aep_ProposedReductioninDCRFDuetoTaxReform_3848D87FCCD2B6AFC6F901C1257B838A" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_ProposedReductioninDCRFDuetoTaxReform_3848D87FCCD2B6AFC6F901C1257B838A" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AnnualRecoveryofStormCoststhroughBaseRates" xlink:label="loc_aep_AnnualRecoveryofStormCoststhroughBaseRates_B3CBCF4532F8D933598B01C1257BED7C" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_AnnualRecoveryofStormCoststhroughBaseRates_B3CBCF4532F8D933598B01C1257BED7C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTexasTotalStormRelatedCosts" xlink:label="loc_aep_AEPTexasTotalStormRelatedCosts_536DC605B39FC1A5E89201C1257B7873" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_AEPTexasTotalStormRelatedCosts_536DC605B39FC1A5E89201C1257B7873" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTexasHurricaneHarveyStormRelatedCosts" xlink:label="loc_aep_AEPTexasHurricaneHarveyStormRelatedCosts_68069729298C9890A4E101C1257B3D6E" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_AEPTexasHurricaneHarveyStormRelatedCosts_68069729298C9890A4E101C1257B3D6E" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTexasHurricaneHarveyStormCapitalExpenditures" xlink:label="loc_aep_AEPTexasHurricaneHarveyStormCapitalExpenditures_B5181F283A86C87CA81101C1257B46AE" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_AEPTexasHurricaneHarveyStormCapitalExpenditures_B5181F283A86C87CA81101C1257B46AE" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_HurricaneHarveyStormInsuranceProceedsReceived" xlink:label="loc_aep_HurricaneHarveyStormInsuranceProceedsReceived_0CB25FA234B23F02C2B601C1257BB1F5" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_HurricaneHarveyStormInsuranceProceedsReceived_0CB25FA234B23F02C2B601C1257BB1F5" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_FuelExpensesNottobeRecovered" xlink:label="loc_aep_FuelExpensesNottobeRecovered_2E1AF5A8322ABA2DA7FD01C1257BD975" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_FuelExpensesNottobeRecovered_2E1AF5A8322ABA2DA7FD01C1257BD975" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ReductioninAnnualBaseRates" xlink:label="loc_aep_ReductioninAnnualBaseRates_3AF6ED76D9DC145F572D01C1257BF480" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_ReductioninAnnualBaseRates_3AF6ED76D9DC145F572D01C1257BF480" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_EnergyEfficiencyProgramsToBeRequestedFromTheVirginiaSCCThroughJuly2028dollars" xlink:label="loc_aep_EnergyEfficiencyProgramsToBeRequestedFromTheVirginiaSCCThroughJuly2028dollars_8C606329973C2B07851101C1257BF40A" xlink:type="locator" />
    <link:definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_EnergyEfficiencyProgramsToBeRequestedFromTheVirginiaSCCThroughJuly2028dollars_8C606329973C2B07851101C1257BF40A" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IntervenorRecommendedReturnOnCommonEquityRange" xlink:label="loc_aep_IntervenorRecommendedReturnOnCommonEquityRange_CD7CBC05E6433ECDFFA401C1257B7787" xlink:type="locator" />
    <link:definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_IntervenorRecommendedReturnOnCommonEquityRange_CD7CBC05E6433ECDFFA401C1257B7787" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ProvisionforRefund" xlink:label="loc_aep_ProvisionforRefund_8932B64E473FC413717101C1257BD804" xlink:type="locator" />
    <link:definitionArc order="15" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_ProvisionforRefund_8932B64E473FC413717101C1257BD804" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AdjustedAnnualIncreaseRequestduetoTaxReform" xlink:label="loc_aep_AdjustedAnnualIncreaseRequestduetoTaxReform_B139CF76ACE911A1A55C01C1257B7F46" xlink:type="locator" />
    <link:definitionArc order="16" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_AdjustedAnnualIncreaseRequestduetoTaxReform_B139CF76ACE911A1A55C01C1257B7F46" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SetlledAnnualIncrease" xlink:label="loc_aep_SetlledAnnualIncrease_8AEF48D992628A0323AA01C1257BB7C3" xlink:type="locator" />
    <link:definitionArc order="17" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_SetlledAnnualIncrease_8AEF48D992628A0323AA01C1257BB7C3" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SettledReturnonCommonEquity" xlink:label="loc_aep_SettledReturnonCommonEquity_9180A07E285148E1BCDC01C1257B8164" xlink:type="locator" />
    <link:definitionArc order="18" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_SettledReturnonCommonEquity_9180A07E285148E1BCDC01C1257B8164" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OriginalSharingofOffSystemSalesMargins" xlink:label="loc_aep_OriginalSharingofOffSystemSalesMargins_0B56A96FF168A02577AC01C1257B50B1" xlink:type="locator" />
    <link:definitionArc order="19" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_OriginalSharingofOffSystemSalesMargins_0B56A96FF168A02577AC01C1257B50B1" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SettledSharingofOffSystemSalesMargins" xlink:label="loc_aep_SettledSharingofOffSystemSalesMargins_2691D999CCBED5BCADA201C1257B0177" xlink:type="locator" />
    <link:definitionArc order="20" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_SettledSharingofOffSystemSalesMargins_2691D999CCBED5BCADA201C1257B0177" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RefundforImpactofTaxReform" xlink:label="loc_aep_RefundforImpactofTaxReform_A8D0C1332DE31E681D7801C1257BC634" xlink:type="locator" />
    <link:definitionArc order="21" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_RefundforImpactofTaxReform_A8D0C1332DE31E681D7801C1257BC634" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RequestedReturnOnEquity" xlink:label="loc_aep_RequestedReturnOnEquity_24D09E26CAB7A0F9157701C1257B2A64" xlink:type="locator" />
    <link:definitionArc order="22" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_RequestedReturnOnEquity_24D09E26CAB7A0F9157701C1257B2A64" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AmountOfAnnualReductionToCustomerBillsThroughCreditAdjustmentRider" xlink:label="loc_aep_AmountOfAnnualReductionToCustomerBillsThroughCreditAdjustmentRider_D9DA437459DDDF89B48C01C1257BDEB0" xlink:type="locator" />
    <link:definitionArc order="23" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_AmountOfAnnualReductionToCustomerBillsThroughCreditAdjustmentRider_D9DA437459DDDF89B48C01C1257BDEB0" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AmountOfIncreasedDepreciationExpenseRequested" xlink:label="loc_aep_AmountOfIncreasedDepreciationExpenseRequested_C65B812248D05B7B309F01C1257B104C" xlink:type="locator" />
    <link:definitionArc order="24" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_AmountOfIncreasedDepreciationExpenseRequested_C65B812248D05B7B309F01C1257B104C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AmountofIncreaseRelatedtoAmortizationofRegulatoryAssets" xlink:label="loc_aep_AmountofIncreaseRelatedtoAmortizationofRegulatoryAssets_0928BFA65C3F06FFCD9B01C1257B6F58" xlink:type="locator" />
    <link:definitionArc order="25" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_AmountofIncreaseRelatedtoAmortizationofRegulatoryAssets_0928BFA65C3F06FFCD9B01C1257B6F58" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ALJRecommendedAnnualIncrease" xlink:label="loc_aep_ALJRecommendedAnnualIncrease_131B63A1C456477E059D01C1257B68D2" xlink:type="locator" />
    <link:definitionArc order="26" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_ALJRecommendedAnnualIncrease_131B63A1C456477E059D01C1257B68D2" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ALJRecommendedReturnonCommonEquity" xlink:label="loc_aep_ALJRecommendedReturnonCommonEquity_FE3CA2AEA61F8F961A9301C1257B3563" xlink:type="locator" />
    <link:definitionArc order="27" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_ALJRecommendedReturnonCommonEquity_FE3CA2AEA61F8F961A9301C1257B3563" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AlternateSupplierCap" xlink:label="loc_aep_AlternateSupplierCap_FD7C76F6FD665091951A01C1257B2067" xlink:type="locator" />
    <link:definitionArc order="28" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_AlternateSupplierCap_FD7C76F6FD665091951A01C1257B2067" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ReducedCapacityChargePretaxLoss" xlink:label="loc_aep_ReducedCapacityChargePretaxLoss_8EF6BA8C76D2AFE384D101C1257B62CC" xlink:type="locator" />
    <link:definitionArc order="29" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_ReducedCapacityChargePretaxLoss_8EF6BA8C76D2AFE384D101C1257B62CC" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ApprovedAnnualRevenueIncrease" xlink:label="loc_aep_ApprovedAnnualRevenueIncrease_17523ACFD8FE081D569201C1257B9F87" xlink:type="locator" />
    <link:definitionArc order="30" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_ApprovedAnnualRevenueIncrease_17523ACFD8FE081D569201C1257B9F87" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ApprovedReturnonCommonEquity" xlink:label="loc_aep_ApprovedReturnonCommonEquity_E2286A9CADD27860F52901C1257BB4AF" xlink:type="locator" />
    <link:definitionArc order="31" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_ApprovedReturnonCommonEquity_E2286A9CADD27860F52901C1257BB4AF" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_KPSCOrderAnnualRevenueIncrease" xlink:label="loc_aep_KPSCOrderAnnualRevenueIncrease_FFBB84C8FAF5D1CEEEB801C1257B340E" xlink:type="locator" />
    <link:definitionArc order="32" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_KPSCOrderAnnualRevenueIncrease_FFBB84C8FAF5D1CEEEB801C1257B340E" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_KPSCOrderReturnonCommonEquity" xlink:label="loc_aep_KPSCOrderReturnonCommonEquity_475684D971EC92E1C64C01C1257B8AAB" xlink:type="locator" />
    <link:definitionArc order="33" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_KPSCOrderReturnonCommonEquity_475684D971EC92E1C64C01C1257B8AAB" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_KPSCOrderAnnualRevenueReductionduetoTaxReform" xlink:label="loc_aep_KPSCOrderAnnualRevenueReductionduetoTaxReform_79E575A4D0B2A02B5D4501C1257B835B" xlink:type="locator" />
    <link:definitionArc order="34" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_KPSCOrderAnnualRevenueReductionduetoTaxReform_79E575A4D0B2A02B5D4501C1257B835B" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_KPSCOrderDeferralofRockportPlantUnitPowerAgreementExpenses" xlink:label="loc_aep_KPSCOrderDeferralofRockportPlantUnitPowerAgreementExpenses_19ED5B6A82A80C05C37A01C1257B6C27" xlink:type="locator" />
    <link:definitionArc order="35" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_KPSCOrderDeferralofRockportPlantUnitPowerAgreementExpenses_19ED5B6A82A80C05C37A01C1257B6C27" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RecoveryReturnofcertainPJMOATTExpensesAboveBelowCorrespondingLevelRecoveredinRates" xlink:label="loc_aep_RecoveryReturnofcertainPJMOATTExpensesAboveBelowCorrespondingLevelRecoveredinRates_2A484691B803B4282DB301C1257B7AB2" xlink:type="locator" />
    <link:definitionArc order="36" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_RecoveryReturnofcertainPJMOATTExpensesAboveBelowCorrespondingLevelRecoveredinRates_2A484691B803B4282DB301C1257B7AB2" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_KPCoRequestforAdditionalRevenueIncrease" xlink:label="loc_aep_KPCoRequestforAdditionalRevenueIncrease_5FA5936585F6A9541A8301C1257B4DF9" xlink:type="locator" />
    <link:definitionArc order="37" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_KPCoRequestforAdditionalRevenueIncrease_5FA5936585F6A9541A8301C1257B4DF9" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_PUCOApprovedReducedCustomerCredits" xlink:label="loc_aep_PUCOApprovedReducedCustomerCredits_A9EB04CB137F4303D88C01C1257B4775" xlink:type="locator" />
    <link:definitionArc order="38" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_PUCOApprovedReducedCustomerCredits_A9EB04CB137F4303D88C01C1257B4775" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ReturnOnCommonEquityPerSettlementAgreement" xlink:label="loc_aep_ReturnOnCommonEquityPerSettlementAgreement_4F083E3458B96D25BD8A01C1257B809F" xlink:type="locator" />
    <link:definitionArc order="39" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_ReturnOnCommonEquityPerSettlementAgreement_4F083E3458B96D25BD8A01C1257B809F" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SolarEnergyProjectsToBeDevelopedAndImplementedBy2021AsProposedInStipulationAgreement" xlink:label="loc_aep_SolarEnergyProjectsToBeDevelopedAndImplementedBy2021AsProposedInStipulationAgreement_3B5FCE63F3B32356923701C1257B7548" xlink:type="locator" />
    <link:definitionArc order="40" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_SolarEnergyProjectsToBeDevelopedAndImplementedBy2021AsProposedInStipulationAgreement_3B5FCE63F3B32356923701C1257B7548" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_WindEnergyProjectsToBeDevelopedAndImplementedBy2021AsProposedInStipulationAgreement" xlink:label="loc_aep_WindEnergyProjectsToBeDevelopedAndImplementedBy2021AsProposedInStipulationAgreement_76442E01A093089A192801C1257B8931" xlink:type="locator" />
    <link:definitionArc order="41" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_WindEnergyProjectsToBeDevelopedAndImplementedBy2021AsProposedInStipulationAgreement_76442E01A093089A192801C1257B8931" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_PercentageofOutputtobeReceivedfromSolarandWindProjectsasProposedinStipulationAgreement" xlink:label="loc_aep_PercentageofOutputtobeReceivedfromSolarandWindProjectsasProposedinStipulationAgreement_180C694C351D96FE49DC01C1257BB858" xlink:type="locator" />
    <link:definitionArc order="42" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_PercentageofOutputtobeReceivedfromSolarandWindProjectsasProposedinStipulationAgreement_180C694C351D96FE49DC01C1257BB858" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MaximumOwnershipPercentageofSolarandWindProjectsasProposedinStipulationAgreement" xlink:label="loc_aep_MaximumOwnershipPercentageofSolarandWindProjectsasProposedinStipulationAgreement_0647B9CAC5FD766E39BE01C1257BE712" xlink:type="locator" />
    <link:definitionArc order="43" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_MaximumOwnershipPercentageofSolarandWindProjectsasProposedinStipulationAgreement_0647B9CAC5FD766E39BE01C1257BE712" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ReturnonCommonEquityProposedintheAmendedESPFiling" xlink:label="loc_aep_ReturnonCommonEquityProposedintheAmendedESPFiling_0D530ACDF3E95762096901C1257B2D60" xlink:type="locator" />
    <link:definitionArc order="44" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_ReturnonCommonEquityProposedintheAmendedESPFiling_0D530ACDF3E95762096901C1257B2D60" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ApprovedAdditionalVegetationManagementExpenses" xlink:label="loc_aep_ApprovedAdditionalVegetationManagementExpenses_063970A4E3AE997488FF01C1257B3F96" xlink:type="locator" />
    <link:definitionArc order="45" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_ApprovedAdditionalVegetationManagementExpenses_063970A4E3AE997488FF01C1257B3F96" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ImpairmentChargeTotal" xlink:label="loc_aep_ImpairmentChargeTotal_47FBE5DDD1B57E833AEC01C1257BD7A2" xlink:type="locator" />
    <link:definitionArc order="46" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_ImpairmentChargeTotal_47FBE5DDD1B57E833AEC01C1257BD7A2" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ImpairmentChargeWelshPlantUnit2" xlink:label="loc_aep_ImpairmentChargeWelshPlantUnit2_74E5B752E26300F593C001C1257B4091" xlink:type="locator" />
    <link:definitionArc order="47" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_ImpairmentChargeWelshPlantUnit2_74E5B752E26300F593C001C1257B4091" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ReturnonCommonEquityFiledinthePendingStipulationAgreement" xlink:label="loc_aep_ReturnonCommonEquityFiledinthePendingStipulationAgreement_87C8CE40C9D94E4A3C3401C1257BC20E" xlink:type="locator" />
    <link:definitionArc order="48" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_ReturnonCommonEquityFiledinthePendingStipulationAgreement_87C8CE40C9D94E4A3C3401C1257BC20E" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RateCapsRelatedtotheDistributionInvestmentRiderRange" xlink:label="loc_aep_RateCapsRelatedtotheDistributionInvestmentRiderRange_913823107A050480AFEF01C1257B24D5" xlink:type="locator" />
    <link:definitionArc order="49" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_RateCapsRelatedtotheDistributionInvestmentRiderRange_913823107A050480AFEF01C1257B24D5" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IntervenorRecommendedRefundtoCustomers" xlink:label="loc_aep_IntervenorRecommendedRefundtoCustomers_FF55468C6148934C394901C1257BBC33" xlink:type="locator" />
    <link:definitionArc order="50" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_IntervenorRecommendedRefundtoCustomers_FF55468C6148934C394901C1257BBC33" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ImpairmentChargeDisallowedPlantInvestments" xlink:label="loc_aep_ImpairmentChargeDisallowedPlantInvestments_3FAD452AD2F204E22DEC01C1257BFBA5" xlink:type="locator" />
    <link:definitionArc order="51" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_ImpairmentChargeDisallowedPlantInvestments_3FAD452AD2F204E22DEC01C1257BFBA5" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AdditionalRevenuesRecognizedtobeSurchargedtoCustomers" xlink:label="loc_aep_AdditionalRevenuesRecognizedtobeSurchargedtoCustomers_6EB4926E811C41B31B1201C1257B3B15" xlink:type="locator" />
    <link:definitionArc order="52" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_AdditionalRevenuesRecognizedtobeSurchargedtoCustomers_6EB4926E811C41B31B1201C1257B3B15" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AdditionalRecognizedExpensesConsistingPrimarilyofDepreciationandVegetationManagement" xlink:label="loc_aep_AdditionalRecognizedExpensesConsistingPrimarilyofDepreciationandVegetationManagement_CC96DD1C4B7D5418D33F01C1257B944C" xlink:type="locator" />
    <link:definitionArc order="53" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_AdditionalRecognizedExpensesConsistingPrimarilyofDepreciationandVegetationManagement_CC96DD1C4B7D5418D33F01C1257B944C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ProposedRevenueReductionDuetoTaxReform" xlink:label="loc_aep_ProposedRevenueReductionDuetoTaxReform_A1EB63AF6CE5E9716D2E01C1257BBD55" xlink:type="locator" />
    <link:definitionArc order="54" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_ProposedRevenueReductionDuetoTaxReform_A1EB63AF6CE5E9716D2E01C1257BBD55" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AmountofLPSCApprovedEligibleWelshPlantEnvironmentalControlDeferredUnrecognizedEquity" xlink:label="loc_aep_AmountofLPSCApprovedEligibleWelshPlantEnvironmentalControlDeferredUnrecognizedEquity_64B44C22E4A1555D0EFE01C1257BF61C" xlink:type="locator" />
    <link:definitionArc order="55" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_AmountofLPSCApprovedEligibleWelshPlantEnvironmentalControlDeferredUnrecognizedEquity_64B44C22E4A1555D0EFE01C1257BF61C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ReturnonCommonEquityInclusiveofRTOPerSettlementAgreement" xlink:label="loc_aep_ReturnonCommonEquityInclusiveofRTOPerSettlementAgreement_5BE40598E204872DACCD01C1257B92DF" xlink:type="locator" />
    <link:definitionArc order="56" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_ReturnonCommonEquityInclusiveofRTOPerSettlementAgreement_5BE40598E204872DACCD01C1257B92DF" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RTOIncentiveAdderPerSettlementAgreement" xlink:label="loc_aep_RTOIncentiveAdderPerSettlementAgreement_938D96DD74C590DC7E5B01C1257B9F73" xlink:type="locator" />
    <link:definitionArc order="57" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_RTOIncentiveAdderPerSettlementAgreement_938D96DD74C590DC7E5B01C1257B9F73" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OneTimeRefundtoCustomersPerSettlementAgreement" xlink:label="loc_aep_OneTimeRefundtoCustomersPerSettlementAgreement_C8436FAC8D473CFD665701C1257B23C5" xlink:type="locator" />
    <link:definitionArc order="58" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_OneTimeRefundtoCustomersPerSettlementAgreement_C8436FAC8D473CFD665701C1257B23C5" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IncreasedCaponEquityPortionoftheCapitalStructurePerSettlementAgreement" xlink:label="loc_aep_IncreasedCaponEquityPortionoftheCapitalStructurePerSettlementAgreement_8CB6CE359A73053E7ACC01C1257BC4F3" xlink:type="locator" />
    <link:definitionArc order="59" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_IncreasedCaponEquityPortionoftheCapitalStructurePerSettlementAgreement_8CB6CE359A73053E7ACC01C1257BC4F3" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OriginalCaponEquityPortionoftheCapitalStructurePriortoSettlementAgreement" xlink:label="loc_aep_OriginalCaponEquityPortionoftheCapitalStructurePriortoSettlementAgreement_9732C46C27603A3CBED501C1257BF9F6" xlink:type="locator" />
    <link:definitionArc order="60" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_OriginalCaponEquityPortionoftheCapitalStructurePriortoSettlementAgreement_9732C46C27603A3CBED501C1257BF9F6" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SecondIntervenorRecommendedReturnonCommonEquity" xlink:label="loc_aep_SecondIntervenorRecommendedReturnonCommonEquity_C3D1C2E0FA7006F779F401C1257B0029" xlink:type="locator" />
    <link:definitionArc order="61" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_SecondIntervenorRecommendedReturnonCommonEquity_C3D1C2E0FA7006F779F401C1257B0029" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SecondIntervenorRecommendedOneTimeRefundtoCustomers" xlink:label="loc_aep_SecondIntervenorRecommendedOneTimeRefundtoCustomers_0A9BAD8186FF457494BF01C1257BB0D4" xlink:type="locator" />
    <link:definitionArc order="62" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_SecondIntervenorRecommendedOneTimeRefundtoCustomers_0A9BAD8186FF457494BF01C1257BB0D4" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_FERCTrialStaffRecommendedReturnonCommonEquity" xlink:label="loc_aep_FERCTrialStaffRecommendedReturnonCommonEquity_9E5F94FD89288D3477A701C1257BC00F" xlink:type="locator" />
    <link:definitionArc order="63" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_FERCTrialStaffRecommendedReturnonCommonEquity_9E5F94FD89288D3477A701C1257BC00F" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ParentOwnershipInterestInETT" xlink:label="loc_aep_ParentOwnershipInterestInETT_4521FC302D2174FDD38A01C1257B4454" xlink:type="locator" />
    <link:definitionArc order="64" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_ParentOwnershipInterestInETT_4521FC302D2174FDD38A01C1257B4454" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPShareOfETTCumulativeRevenuesSubjectToReview" xlink:label="loc_aep_AEPShareOfETTCumulativeRevenuesSubjectToReview_8490165F408ADB34FC3201C1257BDB82" xlink:type="locator" />
    <link:definitionArc order="65" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_AEPShareOfETTCumulativeRevenuesSubjectToReview_8490165F408ADB34FC3201C1257BDB82" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IntervenorRecommendedAnnualIncrease" xlink:label="loc_aep_IntervenorRecommendedAnnualIncrease_37032434F42758A1E02E01C1257B90A7" xlink:type="locator" />
    <link:definitionArc order="66" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_IntervenorRecommendedAnnualIncrease_37032434F42758A1E02E01C1257B90A7" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_A2013ReversalOfPreviouslyRecordedRegulatoryDisallowances" xlink:label="loc_aep_A2013ReversalOfPreviouslyRecordedRegulatoryDisallowances_346FCDCA279969E8351401C1257B3F41" xlink:type="locator" />
    <link:definitionArc order="67" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_A2013ReversalOfPreviouslyRecordedRegulatoryDisallowances_346FCDCA279969E8351401C1257B3F41" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ResultingApprovedBaseRateIncrease" xlink:label="loc_aep_ResultingApprovedBaseRateIncrease_9944B9BEB9F925B1430301C1257B6096" xlink:type="locator" />
    <link:definitionArc order="68" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_ResultingApprovedBaseRateIncrease_9944B9BEB9F925B1430301C1257B6096" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RequestedNetIncreaseinTexasAnnualRevenues" xlink:label="loc_aep_RequestedNetIncreaseinTexasAnnualRevenues_20BA4F17D73C7BB397A501C1257B6C4E" xlink:type="locator" />
    <link:definitionArc order="69" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_RequestedNetIncreaseinTexasAnnualRevenues_20BA4F17D73C7BB397A501C1257B6C4E" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ApprovedNetIncreaseinTexasAnnualRevenues" xlink:label="loc_aep_ApprovedNetIncreaseinTexasAnnualRevenues_4FECB94B1D79289FD13601C1257B8CEE" xlink:type="locator" />
    <link:definitionArc order="70" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_ApprovedNetIncreaseinTexasAnnualRevenues_4FECB94B1D79289FD13601C1257B8CEE" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RequestedAnnualIncrease" xlink:label="loc_aep_RequestedAnnualIncrease_81209C9B613DE8301C6E01C1257BFDAD" xlink:type="locator" />
    <link:definitionArc order="71" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_RequestedAnnualIncrease_81209C9B613DE8301C6E01C1257BFDAD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RegulatoryAssetsNoncurrent" xlink:label="loc_us-gaap_RegulatoryAssetsNoncurrent_67382C0F089BD3EBD75701C1257B986D" xlink:type="locator" />
    <link:definitionArc order="72" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_us-gaap_RegulatoryAssetsNoncurrent_67382C0F089BD3EBD75701C1257B986D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_143AFA22859EF325A10301C1257BE896" xlink:type="locator" />
    <link:definitionArc order="73" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_143AFA22859EF325A10301C1257BE896" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ProjectedCapitalCosts" xlink:label="loc_aep_ProjectedCapitalCosts_28C90FBA9975E258905C01C1257BEE71" xlink:type="locator" />
    <link:definitionArc order="74" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_ProjectedCapitalCosts_28C90FBA9975E258905C01C1257BEE71" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConstructionInProgressGross" xlink:label="loc_us-gaap_ConstructionInProgressGross_AABADBDC05DD927D574001C1257B7804" xlink:type="locator" />
    <link:definitionArc order="75" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_us-gaap_ConstructionInProgressGross_AABADBDC05DD927D574001C1257B7804" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNet" xlink:label="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNet_5340CA56099FD07E9A7D01C1257B03A9" xlink:type="locator" />
    <link:definitionArc order="76" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNet_5340CA56099FD07E9A7D01C1257B03A9" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_TotalAmountofRecoveryRequestedRelatedtoArkansasRetailJurisdictionalShareofEnvironmentalCosts" xlink:label="loc_aep_TotalAmountofRecoveryRequestedRelatedtoArkansasRetailJurisdictionalShareofEnvironmentalCosts_CC6FB7196B0EFBB11C6201C1257B3BE7" xlink:type="locator" />
    <link:definitionArc order="77" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_TotalAmountofRecoveryRequestedRelatedtoArkansasRetailJurisdictionalShareofEnvironmentalCosts_CC6FB7196B0EFBB11C6201C1257B3BE7" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_TotalAmountOfRecoveryRequestedRelatedToLouisianaRetailJurisdictionalShareOfEnvironmentalCosts" xlink:label="loc_aep_TotalAmountOfRecoveryRequestedRelatedToLouisianaRetailJurisdictionalShareOfEnvironmentalCosts_1067DB63AB9886DC79B801C1257B3252" xlink:type="locator" />
    <link:definitionArc order="78" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_TotalAmountOfRecoveryRequestedRelatedToLouisianaRetailJurisdictionalShareOfEnvironmentalCosts_1067DB63AB9886DC79B801C1257B3252" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AmountofLPSCApprovedEligibleWelshPlantEnvironmentalControlDeferrals" xlink:label="loc_aep_AmountofLPSCApprovedEligibleWelshPlantEnvironmentalControlDeferrals_7CC5256242BA31CDEFCD01C1257BCA82" xlink:type="locator" />
    <link:definitionArc order="79" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_AmountofLPSCApprovedEligibleWelshPlantEnvironmentalControlDeferrals_7CC5256242BA31CDEFCD01C1257BCA82" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_FERCTrialStaffRecommendedOneTimeRefundtoCustomers" xlink:label="loc_aep_FERCTrialStaffRecommendedOneTimeRefundtoCustomers_955E18E2D2B955ED358901C1257B74C3" xlink:type="locator" />
    <link:definitionArc order="80" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_C4036AC4BAA96546105E01C1257B3669" xlink:to="loc_aep_FERCTrialStaffRecommendedOneTimeRefundtoCustomers_955E18E2D2B955ED358901C1257B74C3" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/RateMattersTables" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_EAEFA86A904D9F50A606F7E8C126E96A" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_8BD972AC9A582E8F989EF7E8C12603B5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_EAEFA86A904D9F50A606F7E8C126E96A" xlink:to="loc_us-gaap_StatementTable_8BD972AC9A582E8F989EF7E8C12603B5" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_F0D99A6E18DE56911222F7E8C126343C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_8BD972AC9A582E8F989EF7E8C12603B5" xlink:to="loc_dei_LegalEntityAxis_F0D99A6E18DE56911222F7E8C126343C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_81A08E88AF842B4EEB7BF7E8C12610FC_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_F0D99A6E18DE56911222F7E8C126343C" xlink:to="loc_dei_EntityDomain_81A08E88AF842B4EEB7BF7E8C12610FC_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_81A08E88AF842B4EEB7BF7E8C12610FC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_F0D99A6E18DE56911222F7E8C126343C" xlink:to="loc_dei_EntityDomain_81A08E88AF842B4EEB7BF7E8C12610FC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfRegulatoryAssetsTextBlock" xlink:label="loc_us-gaap_ScheduleOfRegulatoryAssetsTextBlock_6FAD566CEDC71B65AEBDF7E8C126A53C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_EAEFA86A904D9F50A606F7E8C126E96A" xlink:to="loc_us-gaap_ScheduleOfRegulatoryAssetsTextBlock_6FAD566CEDC71B65AEBDF7E8C126A53C" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/RateMattersWestCompaniesDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PublicUtilitiesGeneralDisclosuresLineItems" xlink:label="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PublicUtilitiesGeneralDisclosuresTable" xlink:label="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_423C028592597E0F8F2DFD411AFDCDAD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_423C028592597E0F8F2DFD411AFDCDAD" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_5BB54A3A58E0D8476C97FD411AFD56B5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_423C028592597E0F8F2DFD411AFDCDAD" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_5BB54A3A58E0D8476C97FD411AFD56B5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_5F091ED33F5A40A3ABC6FD411AFDE9A9_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_5BB54A3A58E0D8476C97FD411AFD56B5" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_5F091ED33F5A40A3ABC6FD411AFDE9A9_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_5F091ED33F5A40A3ABC6FD411AFDE9A9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_5BB54A3A58E0D8476C97FD411AFD56B5" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_5F091ED33F5A40A3ABC6FD411AFDE9A9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventMember" xlink:label="loc_us-gaap_SubsequentEventMember_F7153B947BA2B468B89AFD411AFE7693" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_5F091ED33F5A40A3ABC6FD411AFDE9A9" xlink:to="loc_us-gaap_SubsequentEventMember_F7153B947BA2B468B89AFD411AFE7693" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_297D6AFFB316ADCDDDBFFD411AFE943C" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_423C028592597E0F8F2DFD411AFDCDAD" xlink:to="loc_us-gaap_RangeAxis_297D6AFFB316ADCDDDBFFD411AFE943C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_4F3BB8D1DAB8A85C5598FD411AFEC9D8_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_297D6AFFB316ADCDDDBFFD411AFE943C" xlink:to="loc_us-gaap_RangeMember_4F3BB8D1DAB8A85C5598FD411AFEC9D8_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_4F3BB8D1DAB8A85C5598FD411AFEC9D8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_297D6AFFB316ADCDDDBFFD411AFE943C" xlink:to="loc_us-gaap_RangeMember_4F3BB8D1DAB8A85C5598FD411AFEC9D8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_F45B55A9B55B4BFC32CAFD411AFE9A63" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_4F3BB8D1DAB8A85C5598FD411AFEC9D8" xlink:to="loc_us-gaap_MinimumMember_F45B55A9B55B4BFC32CAFD411AFE9A63" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_3A361A09CF9CD599878FFD411AFEEF7A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_4F3BB8D1DAB8A85C5598FD411AFEC9D8" xlink:to="loc_us-gaap_MaximumMember_3A361A09CF9CD599878FFD411AFEEF7A" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_BaseRateAxis" xlink:label="loc_aep_BaseRateAxis_6AC900BE95958F270B70FD411AFE40BA" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_423C028592597E0F8F2DFD411AFDCDAD" xlink:to="loc_aep_BaseRateAxis_6AC900BE95958F270B70FD411AFE40BA" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_BaseRateDomain" xlink:label="loc_aep_BaseRateDomain_EA645912A7E88EDF2099FD411AFE9BB6_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_aep_BaseRateAxis_6AC900BE95958F270B70FD411AFE40BA" xlink:to="loc_aep_BaseRateDomain_EA645912A7E88EDF2099FD411AFE9BB6_default" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_BaseRateDomain" xlink:label="loc_aep_BaseRateDomain_EA645912A7E88EDF2099FD411AFE9BB6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_aep_BaseRateAxis_6AC900BE95958F270B70FD411AFE40BA" xlink:to="loc_aep_BaseRateDomain_EA645912A7E88EDF2099FD411AFE9BB6" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTexasInterimTransmissionandDistributionRatesMember" xlink:label="loc_aep_AEPTexasInterimTransmissionandDistributionRatesMember_C7EFEBEE3037D05A4945FD411AFE89F9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_BaseRateDomain_EA645912A7E88EDF2099FD411AFE9BB6" xlink:to="loc_aep_AEPTexasInterimTransmissionandDistributionRatesMember_C7EFEBEE3037D05A4945FD411AFE89F9" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_HurricaneHarveyStormMember" xlink:label="loc_aep_HurricaneHarveyStormMember_D6DCE154C1192740DDD5FD411AFE6D8D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_BaseRateDomain_EA645912A7E88EDF2099FD411AFE9BB6" xlink:to="loc_aep_HurricaneHarveyStormMember_D6DCE154C1192740DDD5FD411AFE6D8D" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ETTInterimTransmissionRatesMember" xlink:label="loc_aep_ETTInterimTransmissionRatesMember_980CC5330C3B3793E501FD411AFEA36D" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_BaseRateDomain_EA645912A7E88EDF2099FD411AFE9BB6" xlink:to="loc_aep_ETTInterimTransmissionRatesMember_980CC5330C3B3793E501FD411AFEA36D" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_A2012TexasBaseRateCaseMember" xlink:label="loc_aep_A2012TexasBaseRateCaseMember_F598CE1E031DF9D9EB4FFD411AFE2FBE" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_BaseRateDomain_EA645912A7E88EDF2099FD411AFE9BB6" xlink:to="loc_aep_A2012TexasBaseRateCaseMember_F598CE1E031DF9D9EB4FFD411AFE2FBE" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_A2016TexasBaseRateCaseMember" xlink:label="loc_aep_A2016TexasBaseRateCaseMember_55D600CF57894807A57FFD411AFE8633" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_BaseRateDomain_EA645912A7E88EDF2099FD411AFE9BB6" xlink:to="loc_aep_A2016TexasBaseRateCaseMember_55D600CF57894807A57FFD411AFE8633" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_Louisiana2015FormulaRateFilingMember" xlink:label="loc_aep_Louisiana2015FormulaRateFilingMember_EC5D1DB783F93873D3DBFD411AFF5D95" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_BaseRateDomain_EA645912A7E88EDF2099FD411AFE9BB6" xlink:to="loc_aep_Louisiana2015FormulaRateFilingMember_EC5D1DB783F93873D3DBFD411AFF5D95" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_Louisiana2017FormulaRateFilingMember" xlink:label="loc_aep_Louisiana2017FormulaRateFilingMember_887E1A45AF57BDD3774CFD411AFF74E6" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_BaseRateDomain_EA645912A7E88EDF2099FD411AFE9BB6" xlink:to="loc_aep_Louisiana2017FormulaRateFilingMember_887E1A45AF57BDD3774CFD411AFF74E6" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_Louisiana2018FormulaRateFilingMember" xlink:label="loc_aep_Louisiana2018FormulaRateFilingMember_FCF859B650BA2AF97EF7FD411AFF9C9B" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_BaseRateDomain_EA645912A7E88EDF2099FD411AFE9BB6" xlink:to="loc_aep_Louisiana2018FormulaRateFilingMember_FCF859B650BA2AF97EF7FD411AFF9C9B" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_WelshPlantUnits1And3EnvironmentalProjectsMember" xlink:label="loc_aep_WelshPlantUnits1And3EnvironmentalProjectsMember_A0161DD25AE0877CB2F2FD411AFF68E5" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_BaseRateDomain_EA645912A7E88EDF2099FD411AFE9BB6" xlink:to="loc_aep_WelshPlantUnits1And3EnvironmentalProjectsMember_A0161DD25AE0877CB2F2FD411AFF68E5" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_FERCTransmissionComplaintAEPSPPParticipantsMember" xlink:label="loc_aep_FERCTransmissionComplaintAEPSPPParticipantsMember_AF91982CCD6CB2A1F352FD411AFF0B3F" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_BaseRateDomain_EA645912A7E88EDF2099FD411AFE9BB6" xlink:to="loc_aep_FERCTransmissionComplaintAEPSPPParticipantsMember_AF91982CCD6CB2A1F352FD411AFF0B3F" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_FERCSWEPCoPowerSupplyAgreementsComplaintMember" xlink:label="loc_aep_FERCSWEPCoPowerSupplyAgreementsComplaintMember_F2D697E96F0785C918D5FD411AFF848C" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_BaseRateDomain_EA645912A7E88EDF2099FD411AFE9BB6" xlink:to="loc_aep_FERCSWEPCoPowerSupplyAgreementsComplaintMember_F2D697E96F0785C918D5FD411AFF848C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PublicUtilityAxis" xlink:label="loc_us-gaap_PublicUtilityAxis_12A1A3B9BDE4C18BC840FD411AFF2419" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_423C028592597E0F8F2DFD411AFDCDAD" xlink:to="loc_us-gaap_PublicUtilityAxis_12A1A3B9BDE4C18BC840FD411AFF2419" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_UtilityPlantDomain" xlink:label="loc_us-gaap_UtilityPlantDomain_755420480C5D24DD08E1FD411AFF410E_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PublicUtilityAxis_12A1A3B9BDE4C18BC840FD411AFF2419" xlink:to="loc_us-gaap_UtilityPlantDomain_755420480C5D24DD08E1FD411AFF410E_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_UtilityPlantDomain" xlink:label="loc_us-gaap_UtilityPlantDomain_755420480C5D24DD08E1FD411AFF410E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PublicUtilityAxis_12A1A3B9BDE4C18BC840FD411AFF2419" xlink:to="loc_us-gaap_UtilityPlantDomain_755420480C5D24DD08E1FD411AFF410E" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_WelshPlantUnit1and3Member" xlink:label="loc_aep_WelshPlantUnit1and3Member_E4D4962478DE6FEFEEA0FD411AFFD82A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_UtilityPlantDomain_755420480C5D24DD08E1FD411AFF410E" xlink:to="loc_aep_WelshPlantUnit1and3Member_E4D4962478DE6FEFEEA0FD411AFFD82A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_994965AEFCFFCDE0CB52FD411AFF16FE" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresTable_423C028592597E0F8F2DFD411AFDCDAD" xlink:to="loc_dei_LegalEntityAxis_994965AEFCFFCDE0CB52FD411AFF16FE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_04E298AEB34C5D748386FD411AFF2453_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_994965AEFCFFCDE0CB52FD411AFF16FE" xlink:to="loc_dei_EntityDomain_04E298AEB34C5D748386FD411AFF2453_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_04E298AEB34C5D748386FD411AFF2453" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_994965AEFCFFCDE0CB52FD411AFF16FE" xlink:to="loc_dei_EntityDomain_04E298AEB34C5D748386FD411AFF2453" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTexasInc.Member" xlink:label="loc_aep_AEPTexasInc.Member_13CB7E0BFC83E591C1DAFD411AFF5313" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_04E298AEB34C5D748386FD411AFF2453" xlink:to="loc_aep_AEPTexasInc.Member_13CB7E0BFC83E591C1DAFD411AFF5313" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_PublicServiceCoOfOklahomaMember" xlink:label="loc_aep_PublicServiceCoOfOklahomaMember_0B4B89DC4A7A64158E72FD411AFFD9E4" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_04E298AEB34C5D748386FD411AFF2453" xlink:to="loc_aep_PublicServiceCoOfOklahomaMember_0B4B89DC4A7A64158E72FD411AFFD9E4" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SouthwesternElectricPowerCoMember" xlink:label="loc_aep_SouthwesternElectricPowerCoMember_2C0D9860F74A9C6F4BBAFD411AFF6E99" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_04E298AEB34C5D748386FD411AFF2453" xlink:to="loc_aep_SouthwesternElectricPowerCoMember_2C0D9860F74A9C6F4BBAFD411AFF6E99" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTexasCumulativeRevenuesSubjecttoReview" xlink:label="loc_aep_AEPTexasCumulativeRevenuesSubjecttoReview_CC990E6351C37454E3C3FD411B00E538" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_AEPTexasCumulativeRevenuesSubjecttoReview_CC990E6351C37454E3C3FD411B00E538" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ProposedReductioninTransmissionRatesDuetoTaxReform" xlink:label="loc_aep_ProposedReductioninTransmissionRatesDuetoTaxReform_0B9ECF1B01C7B66D14EAFD411B007AE7" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_ProposedReductioninTransmissionRatesDuetoTaxReform_0B9ECF1B01C7B66D14EAFD411B007AE7" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ProposedNetIncreaseinDCRF" xlink:label="loc_aep_ProposedNetIncreaseinDCRF_98AF19AE4A3B612AE8AEFD411B001D61" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_ProposedNetIncreaseinDCRF_98AF19AE4A3B612AE8AEFD411B001D61" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ProposedIncreaseinDCRFDuetoCapitalInvestments" xlink:label="loc_aep_ProposedIncreaseinDCRFDuetoCapitalInvestments_362F345CA985127A53A3FD411B00688B" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_ProposedIncreaseinDCRFDuetoCapitalInvestments_362F345CA985127A53A3FD411B00688B" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ProposedReductioninDCRFDuetoTaxReform" xlink:label="loc_aep_ProposedReductioninDCRFDuetoTaxReform_A9FA7563D057F5E9F5C9FD411B0035CA" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_ProposedReductioninDCRFDuetoTaxReform_A9FA7563D057F5E9F5C9FD411B0035CA" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AnnualRecoveryofStormCoststhroughBaseRates" xlink:label="loc_aep_AnnualRecoveryofStormCoststhroughBaseRates_3CB28BC3F3F9896E2481FD411B00DF78" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_AnnualRecoveryofStormCoststhroughBaseRates_3CB28BC3F3F9896E2481FD411B00DF78" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTexasTotalStormRelatedCosts" xlink:label="loc_aep_AEPTexasTotalStormRelatedCosts_93D695A77ECEEF15B189FD411B0109CA" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_AEPTexasTotalStormRelatedCosts_93D695A77ECEEF15B189FD411B0109CA" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTexasHurricaneHarveyStormRelatedCosts" xlink:label="loc_aep_AEPTexasHurricaneHarveyStormRelatedCosts_5CEC3D0A75875A5958E0FD411B01A812" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_AEPTexasHurricaneHarveyStormRelatedCosts_5CEC3D0A75875A5958E0FD411B01A812" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTexasHurricaneHarveyStormCapitalExpenditures" xlink:label="loc_aep_AEPTexasHurricaneHarveyStormCapitalExpenditures_08D04EFA36A21078A1CCFD411B017860" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_AEPTexasHurricaneHarveyStormCapitalExpenditures_08D04EFA36A21078A1CCFD411B017860" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_HurricaneHarveyStormInsuranceProceedsReceived" xlink:label="loc_aep_HurricaneHarveyStormInsuranceProceedsReceived_05B8DF4394AD84DE1F47FD411B01EEBE" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_HurricaneHarveyStormInsuranceProceedsReceived_05B8DF4394AD84DE1F47FD411B01EEBE" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ParentOwnershipInterestInETT" xlink:label="loc_aep_ParentOwnershipInterestInETT_4795F0D6ED322A74B22FFD411B01D27C" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_ParentOwnershipInterestInETT_4795F0D6ED322A74B22FFD411B01D27C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPShareOfETTCumulativeRevenuesSubjectToReview" xlink:label="loc_aep_AEPShareOfETTCumulativeRevenuesSubjectToReview_BDDAAA28D8AB898CEA41FD411B010CA6" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_AEPShareOfETTCumulativeRevenuesSubjectToReview_BDDAAA28D8AB898CEA41FD411B010CA6" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_A2013ReversalOfPreviouslyRecordedRegulatoryDisallowances" xlink:label="loc_aep_A2013ReversalOfPreviouslyRecordedRegulatoryDisallowances_1D47D1F5A81C9610EC5DFD411B0168C4" xlink:type="locator" />
    <link:definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_A2013ReversalOfPreviouslyRecordedRegulatoryDisallowances_1D47D1F5A81C9610EC5DFD411B0168C4" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ResultingApprovedBaseRateIncrease" xlink:label="loc_aep_ResultingApprovedBaseRateIncrease_7DDF736891222E6C6D46FD411B01BF9D" xlink:type="locator" />
    <link:definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_ResultingApprovedBaseRateIncrease_7DDF736891222E6C6D46FD411B01BF9D" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RequestedNetIncreaseinTexasAnnualRevenues" xlink:label="loc_aep_RequestedNetIncreaseinTexasAnnualRevenues_6333D265092CCEC411FFFD411B01D0CA" xlink:type="locator" />
    <link:definitionArc order="15" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_RequestedNetIncreaseinTexasAnnualRevenues_6333D265092CCEC411FFFD411B01D0CA" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RequestedReturnOnEquity" xlink:label="loc_aep_RequestedReturnOnEquity_58CD52350860E57A5E81FD411B01DA4E" xlink:type="locator" />
    <link:definitionArc order="16" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_RequestedReturnOnEquity_58CD52350860E57A5E81FD411B01DA4E" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ApprovedNetIncreaseinTexasAnnualRevenues" xlink:label="loc_aep_ApprovedNetIncreaseinTexasAnnualRevenues_85F6EFFE8A2A3AA7F87FFD411B01A0FC" xlink:type="locator" />
    <link:definitionArc order="17" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_ApprovedNetIncreaseinTexasAnnualRevenues_85F6EFFE8A2A3AA7F87FFD411B01A0FC" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ApprovedReturnonCommonEquity" xlink:label="loc_aep_ApprovedReturnonCommonEquity_9CE73EED2C2B695BDF43FD411B0154B4" xlink:type="locator" />
    <link:definitionArc order="18" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_ApprovedReturnonCommonEquity_9CE73EED2C2B695BDF43FD411B0154B4" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ApprovedAdditionalVegetationManagementExpenses" xlink:label="loc_aep_ApprovedAdditionalVegetationManagementExpenses_2AB6B5D0E0FC1BE6C3A4FD411B0223ED" xlink:type="locator" />
    <link:definitionArc order="19" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_ApprovedAdditionalVegetationManagementExpenses_2AB6B5D0E0FC1BE6C3A4FD411B0223ED" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ImpairmentChargeTotal" xlink:label="loc_aep_ImpairmentChargeTotal_9B76FEC7F85A1325CD47FD411B02BA3A" xlink:type="locator" />
    <link:definitionArc order="20" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_ImpairmentChargeTotal_9B76FEC7F85A1325CD47FD411B02BA3A" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ImpairmentChargeWelshPlantUnit2" xlink:label="loc_aep_ImpairmentChargeWelshPlantUnit2_BD036319D7E1C8FD30C8FD411B02D260" xlink:type="locator" />
    <link:definitionArc order="21" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_ImpairmentChargeWelshPlantUnit2_BD036319D7E1C8FD30C8FD411B02D260" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ImpairmentChargeDisallowedPlantInvestments" xlink:label="loc_aep_ImpairmentChargeDisallowedPlantInvestments_00A7879083FE1D8162F2FD411B021E1A" xlink:type="locator" />
    <link:definitionArc order="22" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_ImpairmentChargeDisallowedPlantInvestments_00A7879083FE1D8162F2FD411B021E1A" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AdditionalRevenuesRecognizedtobeSurchargedtoCustomers" xlink:label="loc_aep_AdditionalRevenuesRecognizedtobeSurchargedtoCustomers_F61CC67D556FD0CBFFD5FD411B021A0C" xlink:type="locator" />
    <link:definitionArc order="23" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_AdditionalRevenuesRecognizedtobeSurchargedtoCustomers_F61CC67D556FD0CBFFD5FD411B021A0C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AdditionalRecognizedExpensesConsistingPrimarilyofDepreciationandVegetationManagement" xlink:label="loc_aep_AdditionalRecognizedExpensesConsistingPrimarilyofDepreciationandVegetationManagement_1BDC04279DEDADBC451DFD411B029624" xlink:type="locator" />
    <link:definitionArc order="24" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_AdditionalRecognizedExpensesConsistingPrimarilyofDepreciationandVegetationManagement_1BDC04279DEDADBC451DFD411B029624" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ProposedRevenueReductionDuetoTaxReform" xlink:label="loc_aep_ProposedRevenueReductionDuetoTaxReform_24C900367DE47A93FB96FD411B022FDC" xlink:type="locator" />
    <link:definitionArc order="25" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_ProposedRevenueReductionDuetoTaxReform_24C900367DE47A93FB96FD411B022FDC" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RequestedAnnualIncrease" xlink:label="loc_aep_RequestedAnnualIncrease_BAC9867FE0A66A0D3736FD411B025D2C" xlink:type="locator" />
    <link:definitionArc order="26" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_RequestedAnnualIncrease_BAC9867FE0A66A0D3736FD411B025D2C" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ProjectedCapitalCosts" xlink:label="loc_aep_ProjectedCapitalCosts_CA5CBE3AE976974DF59AFD411B022C93" xlink:type="locator" />
    <link:definitionArc order="27" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_ProjectedCapitalCosts_CA5CBE3AE976974DF59AFD411B022C93" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConstructionInProgressGross" xlink:label="loc_us-gaap_ConstructionInProgressGross_A16B00A363E296A08C6DFD411B022573" xlink:type="locator" />
    <link:definitionArc order="28" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_us-gaap_ConstructionInProgressGross_A16B00A363E296A08C6DFD411B022573" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNet" xlink:label="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNet_21ACA9521E361A89E0DEFD411B02C1F7" xlink:type="locator" />
    <link:definitionArc order="29" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNet_21ACA9521E361A89E0DEFD411B02C1F7" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_TotalAmountofRecoveryRequestedRelatedtoArkansasRetailJurisdictionalShareofEnvironmentalCosts" xlink:label="loc_aep_TotalAmountofRecoveryRequestedRelatedtoArkansasRetailJurisdictionalShareofEnvironmentalCosts_62AED10FC21C2B3D862AFD411B025F9B" xlink:type="locator" />
    <link:definitionArc order="30" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_TotalAmountofRecoveryRequestedRelatedtoArkansasRetailJurisdictionalShareofEnvironmentalCosts_62AED10FC21C2B3D862AFD411B025F9B" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_TotalAmountOfRecoveryRequestedRelatedToLouisianaRetailJurisdictionalShareOfEnvironmentalCosts" xlink:label="loc_aep_TotalAmountOfRecoveryRequestedRelatedToLouisianaRetailJurisdictionalShareOfEnvironmentalCosts_56E1CD5D48E026A029A8FD411B02B7C6" xlink:type="locator" />
    <link:definitionArc order="31" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_TotalAmountOfRecoveryRequestedRelatedToLouisianaRetailJurisdictionalShareOfEnvironmentalCosts_56E1CD5D48E026A029A8FD411B02B7C6" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AmountofLPSCApprovedEligibleWelshPlantEnvironmentalControlDeferrals" xlink:label="loc_aep_AmountofLPSCApprovedEligibleWelshPlantEnvironmentalControlDeferrals_0C5B31B6F0E58DF8A722FD411B026532" xlink:type="locator" />
    <link:definitionArc order="32" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_AmountofLPSCApprovedEligibleWelshPlantEnvironmentalControlDeferrals_0C5B31B6F0E58DF8A722FD411B026532" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AmountofLPSCApprovedEligibleWelshPlantEnvironmentalControlDeferredUnrecognizedEquity" xlink:label="loc_aep_AmountofLPSCApprovedEligibleWelshPlantEnvironmentalControlDeferredUnrecognizedEquity_93EF587C7D9DEABB40BAFD411B023F7E" xlink:type="locator" />
    <link:definitionArc order="33" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_AmountofLPSCApprovedEligibleWelshPlantEnvironmentalControlDeferredUnrecognizedEquity_93EF587C7D9DEABB40BAFD411B023F7E" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IntervenorRecommendedReturnOnCommonEquityRange" xlink:label="loc_aep_IntervenorRecommendedReturnOnCommonEquityRange_E3014B7557A00942FCD2FD411B034DDC" xlink:type="locator" />
    <link:definitionArc order="34" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesGeneralDisclosuresLineItems_05C7507ABC802D3A3F40FD411B00C294" xlink:to="loc_aep_IntervenorRecommendedReturnOnCommonEquityRange_E3014B7557A00942FCD2FD411B034DDC" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/RevenueFromContractsWithCustomersDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_DC95D119BAECE4A9C4C2F8493417AEBF" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_761969541FC80837BF96F849341248ED" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_DC95D119BAECE4A9C4C2F8493417AEBF" xlink:to="loc_us-gaap_StatementTable_761969541FC80837BF96F849341248ED" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_C17D75109F886150D262F84934130B3A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_761969541FC80837BF96F849341248ED" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_C17D75109F886150D262F84934130B3A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_13C63F44AAFEA45BDDF7F8493413073A_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_C17D75109F886150D262F84934130B3A" xlink:to="loc_us-gaap_SegmentDomain_13C63F44AAFEA45BDDF7F8493413073A_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_13C63F44AAFEA45BDDF7F8493413073A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_C17D75109F886150D262F84934130B3A" xlink:to="loc_us-gaap_SegmentDomain_13C63F44AAFEA45BDDF7F8493413073A" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_VerticallyIntegratedUtilitiesMember" xlink:label="loc_aep_VerticallyIntegratedUtilitiesMember_7A7013C75429DC2EBD17F84934135C81" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_13C63F44AAFEA45BDDF7F8493413073A" xlink:to="loc_aep_VerticallyIntegratedUtilitiesMember_7A7013C75429DC2EBD17F84934135C81" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_TransmissionAndDistributionCompaniesMember" xlink:label="loc_aep_TransmissionAndDistributionCompaniesMember_173909DC67F1D213D832F84934148E8B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_13C63F44AAFEA45BDDF7F8493413073A" xlink:to="loc_aep_TransmissionAndDistributionCompaniesMember_173909DC67F1D213D832F84934148E8B" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTransmissionHoldcoMember" xlink:label="loc_aep_AEPTransmissionHoldcoMember_45AFF61335042902AE4AF849341401EC" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_13C63F44AAFEA45BDDF7F8493413073A" xlink:to="loc_aep_AEPTransmissionHoldcoMember_45AFF61335042902AE4AF849341401EC" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_GenerationAndMarketingMember" xlink:label="loc_aep_GenerationAndMarketingMember_0E869C2460A022BD9995F84934141E35" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_13C63F44AAFEA45BDDF7F8493413073A" xlink:to="loc_aep_GenerationAndMarketingMember_0E869C2460A022BD9995F84934141E35" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AllOtherSegmentsMember" xlink:label="loc_us-gaap_AllOtherSegmentsMember_014A6B52C3F810257D01F8493414CEDF" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_13C63F44AAFEA45BDDF7F8493413073A" xlink:to="loc_us-gaap_AllOtherSegmentsMember_014A6B52C3F810257D01F8493414CEDF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationItemsAxis" xlink:label="loc_us-gaap_ConsolidationItemsAxis_246F0F8B3A2445CCC3F1F8493414959F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_761969541FC80837BF96F849341248ED" xlink:to="loc_us-gaap_ConsolidationItemsAxis_246F0F8B3A2445CCC3F1F8493414959F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationItemsDomain" xlink:label="loc_us-gaap_ConsolidationItemsDomain_A846D3C19D08AAF4235CF84934142A4D_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConsolidationItemsAxis_246F0F8B3A2445CCC3F1F8493414959F" xlink:to="loc_us-gaap_ConsolidationItemsDomain_A846D3C19D08AAF4235CF84934142A4D_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationItemsDomain" xlink:label="loc_us-gaap_ConsolidationItemsDomain_A846D3C19D08AAF4235CF84934142A4D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConsolidationItemsAxis_246F0F8B3A2445CCC3F1F8493414959F" xlink:to="loc_us-gaap_ConsolidationItemsDomain_A846D3C19D08AAF4235CF84934142A4D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationEliminationsMember" xlink:label="loc_us-gaap_ConsolidationEliminationsMember_9361A6CB775CEE9D6A7EF84934144FA3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidationItemsDomain_A846D3C19D08AAF4235CF84934142A4D" xlink:to="loc_us-gaap_ConsolidationEliminationsMember_9361A6CB775CEE9D6A7EF84934144FA3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_79ED79F6412479C30FE8F84934146628" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_761969541FC80837BF96F849341248ED" xlink:to="loc_dei_LegalEntityAxis_79ED79F6412479C30FE8F84934146628" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_E2A88477D6DC410C38B4F8493414996F_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_79ED79F6412479C30FE8F84934146628" xlink:to="loc_dei_EntityDomain_E2A88477D6DC410C38B4F8493414996F_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_E2A88477D6DC410C38B4F8493414996F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_79ED79F6412479C30FE8F84934146628" xlink:to="loc_dei_EntityDomain_E2A88477D6DC410C38B4F8493414996F" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTexasInc.Member" xlink:label="loc_aep_AEPTexasInc.Member_2323C09A92E1B0E81544F84934144E3F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_E2A88477D6DC410C38B4F8493414996F" xlink:to="loc_aep_AEPTexasInc.Member_2323C09A92E1B0E81544F84934144E3F" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTransmissionCoMember" xlink:label="loc_aep_AEPTransmissionCoMember_98B5F94748C6AAB3CF08F8493414C8C2" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_E2A88477D6DC410C38B4F8493414996F" xlink:to="loc_aep_AEPTransmissionCoMember_98B5F94748C6AAB3CF08F8493414C8C2" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AppalachianPowerCoMember" xlink:label="loc_aep_AppalachianPowerCoMember_17C94CD9E5D2E31DE6F8F84934159BC9" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_E2A88477D6DC410C38B4F8493414996F" xlink:to="loc_aep_AppalachianPowerCoMember_17C94CD9E5D2E31DE6F8F84934159BC9" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IndianaMichiganPowerCoMember" xlink:label="loc_aep_IndianaMichiganPowerCoMember_C4149F811A71FDCC3F7AF84934159F5E" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_E2A88477D6DC410C38B4F8493414996F" xlink:to="loc_aep_IndianaMichiganPowerCoMember_C4149F811A71FDCC3F7AF84934159F5E" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OhioPowerCoMember" xlink:label="loc_aep_OhioPowerCoMember_D7BDFC337D5B0CCC7EDFF8493415577E" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_E2A88477D6DC410C38B4F8493414996F" xlink:to="loc_aep_OhioPowerCoMember_D7BDFC337D5B0CCC7EDFF8493415577E" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_PublicServiceCoOfOklahomaMember" xlink:label="loc_aep_PublicServiceCoOfOklahomaMember_D7E331B1810C16084E8FF8493415C53B" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_E2A88477D6DC410C38B4F8493414996F" xlink:to="loc_aep_PublicServiceCoOfOklahomaMember_D7E331B1810C16084E8FF8493415C53B" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_SouthwesternElectricPowerCoMember" xlink:label="loc_aep_SouthwesternElectricPowerCoMember_2E5D0E79C27519E2B42EF8493415C472" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_E2A88477D6DC410C38B4F8493414996F" xlink:to="loc_aep_SouthwesternElectricPowerCoMember_2E5D0E79C27519E2B42EF8493415C472" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProductOrServiceAxis" xlink:label="loc_us-gaap_ProductOrServiceAxis_0A30855256F11C429A01F84934152B46" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_761969541FC80837BF96F849341248ED" xlink:to="loc_us-gaap_ProductOrServiceAxis_0A30855256F11C429A01F84934152B46" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProductsAndServicesDomain" xlink:label="loc_us-gaap_ProductsAndServicesDomain_D56B002292923601B760F84934156940_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ProductOrServiceAxis_0A30855256F11C429A01F84934152B46" xlink:to="loc_us-gaap_ProductsAndServicesDomain_D56B002292923601B760F84934156940_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProductsAndServicesDomain" xlink:label="loc_us-gaap_ProductsAndServicesDomain_D56B002292923601B760F84934156940" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ProductOrServiceAxis_0A30855256F11C429A01F84934152B46" xlink:to="loc_us-gaap_ProductsAndServicesDomain_D56B002292923601B760F84934156940" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RetailMember" xlink:label="loc_aep_RetailMember_7C630F83F59108D5CA91F84934159676" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_D56B002292923601B760F84934156940" xlink:to="loc_aep_RetailMember_7C630F83F59108D5CA91F84934159676" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ResidentialMember" xlink:label="loc_aep_ResidentialMember_723F7D5887E712516A6AF8493415D55A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_RetailMember_7C630F83F59108D5CA91F84934159676" xlink:to="loc_aep_ResidentialMember_723F7D5887E712516A6AF8493415D55A" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_CommercialMember" xlink:label="loc_aep_CommercialMember_00C0E5E038E92D1ACADDF849341553B0" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_RetailMember_7C630F83F59108D5CA91F84934159676" xlink:to="loc_aep_CommercialMember_00C0E5E038E92D1ACADDF849341553B0" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_IndustrialMember" xlink:label="loc_aep_IndustrialMember_2A11AABC8D429E59BC21F84934159BEF" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_RetailMember_7C630F83F59108D5CA91F84934159676" xlink:to="loc_aep_IndustrialMember_2A11AABC8D429E59BC21F84934159BEF" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OtherRetailMember" xlink:label="loc_aep_OtherRetailMember_7B5EDAA0F851C2ECDA95F8493415BAB9" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_RetailMember_7C630F83F59108D5CA91F84934159676" xlink:to="loc_aep_OtherRetailMember_7B5EDAA0F851C2ECDA95F8493415BAB9" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_WholesaleandCompetitiveMember" xlink:label="loc_aep_WholesaleandCompetitiveMember_66284DE91BCA9B6AC2F2F849341609CA" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_D56B002292923601B760F84934156940" xlink:to="loc_aep_WholesaleandCompetitiveMember_66284DE91BCA9B6AC2F2F849341609CA" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_GenerationMember" xlink:label="loc_aep_GenerationMember_B39AB54BB8D798EA8A97F8493416E565" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_WholesaleandCompetitiveMember_66284DE91BCA9B6AC2F2F849341609CA" xlink:to="loc_aep_GenerationMember_B39AB54BB8D798EA8A97F8493416E565" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_GenerationAffiliatedMember" xlink:label="loc_aep_GenerationAffiliatedMember_B39F9BDA3CAAED30A0F8F84934163B71" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_WholesaleandCompetitiveMember_66284DE91BCA9B6AC2F2F849341609CA" xlink:to="loc_aep_GenerationAffiliatedMember_B39F9BDA3CAAED30A0F8F84934163B71" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_TransmissionMember" xlink:label="loc_aep_TransmissionMember_D3F58140357E67B66208F84934161C0D" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_WholesaleandCompetitiveMember_66284DE91BCA9B6AC2F2F849341609CA" xlink:to="loc_aep_TransmissionMember_D3F58140357E67B66208F84934161C0D" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_TransmissionAffiliatedMember" xlink:label="loc_aep_TransmissionAffiliatedMember_D656D0FAD281E4B0E914F849341618DD" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_WholesaleandCompetitiveMember_66284DE91BCA9B6AC2F2F849341609CA" xlink:to="loc_aep_TransmissionAffiliatedMember_D656D0FAD281E4B0E914F849341618DD" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_MarketingCompetitiveRetailandRenewableMember" xlink:label="loc_aep_MarketingCompetitiveRetailandRenewableMember_8F7CAC16C3C21D370C9AF8493416441B" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_WholesaleandCompetitiveMember_66284DE91BCA9B6AC2F2F849341609CA" xlink:to="loc_aep_MarketingCompetitiveRetailandRenewableMember_8F7CAC16C3C21D370C9AF8493416441B" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OtherRevenuesMember" xlink:label="loc_aep_OtherRevenuesMember_D8CBC2938FDB67488CE4F8493416C899" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_D56B002292923601B760F84934156940" xlink:to="loc_aep_OtherRevenuesMember_D8CBC2938FDB67488CE4F8493416C899" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OtherRevenuesAffiliatedMember" xlink:label="loc_aep_OtherRevenuesAffiliatedMember_07E8A0CCAE50A41CFC38F849341612FD" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_D56B002292923601B760F84934156940" xlink:to="loc_aep_OtherRevenuesAffiliatedMember_07E8A0CCAE50A41CFC38F849341612FD" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AlternativeandOtherMember" xlink:label="loc_aep_AlternativeandOtherMember_6C07D34BB37C0ACB7041F8493416E050" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain_D56B002292923601B760F84934156940" xlink:to="loc_aep_AlternativeandOtherMember_6C07D34BB37C0ACB7041F8493416E050" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AlternativeMember" xlink:label="loc_aep_AlternativeMember_6E8157066BC593FAA3A0F8493416FCE8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_AlternativeandOtherMember_6C07D34BB37C0ACB7041F8493416E050" xlink:to="loc_aep_AlternativeMember_6E8157066BC593FAA3A0F8493416FCE8" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RecognitionPeriodAxis" xlink:label="loc_aep_RecognitionPeriodAxis_B92C6332BF91F914E834F84934165697" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_761969541FC80837BF96F849341248ED" xlink:to="loc_aep_RecognitionPeriodAxis_B92C6332BF91F914E834F84934165697" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RecognitionPeriodDomain" xlink:label="loc_aep_RecognitionPeriodDomain_2D951473A6236DC5644CF8493416B5F1_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_aep_RecognitionPeriodAxis_B92C6332BF91F914E834F84934165697" xlink:to="loc_aep_RecognitionPeriodDomain_2D951473A6236DC5644CF8493416B5F1_default" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RecognitionPeriodDomain" xlink:label="loc_aep_RecognitionPeriodDomain_2D951473A6236DC5644CF8493416B5F1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_aep_RecognitionPeriodAxis_B92C6332BF91F914E834F84934165697" xlink:to="loc_aep_RecognitionPeriodDomain_2D951473A6236DC5644CF8493416B5F1" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_LessThan1YearMember" xlink:label="loc_aep_LessThan1YearMember_496BCE9B5F5434D70EB7F84934172386" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_RecognitionPeriodDomain_2D951473A6236DC5644CF8493416B5F1" xlink:to="loc_aep_LessThan1YearMember_496BCE9B5F5434D70EB7F84934172386" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_A23YearsMember" xlink:label="loc_aep_A23YearsMember_15A546C797D2D5B1356CF84934176430" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_RecognitionPeriodDomain_2D951473A6236DC5644CF8493416B5F1" xlink:to="loc_aep_A23YearsMember_15A546C797D2D5B1356CF84934176430" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_A45YearsMember" xlink:label="loc_aep_A45YearsMember_2A6AADE238B9C1D81253F84934173693" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_RecognitionPeriodDomain_2D951473A6236DC5644CF8493416B5F1" xlink:to="loc_aep_A45YearsMember_2A6AADE238B9C1D81253F84934173693" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_After5YearsMember" xlink:label="loc_aep_After5YearsMember_4CDA09FCDED5B629B5C0F84934179197" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_RecognitionPeriodDomain_2D951473A6236DC5644CF8493416B5F1" xlink:to="loc_aep_After5YearsMember_4CDA09FCDED5B629B5C0F84934179197" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ContractWithCustomerDurationAxis" xlink:label="loc_us-gaap_ContractWithCustomerDurationAxis_CF972923A2E199B893EEF84FA42FA6E2" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_761969541FC80837BF96F849341248ED" xlink:to="loc_us-gaap_ContractWithCustomerDurationAxis_CF972923A2E199B893EEF84FA42FA6E2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ContractWithCustomerDurationDomain" xlink:label="loc_us-gaap_ContractWithCustomerDurationDomain_C0393B7F3CDCA0849D81F84FF69B8950_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ContractWithCustomerDurationAxis_CF972923A2E199B893EEF84FA42FA6E2" xlink:to="loc_us-gaap_ContractWithCustomerDurationDomain_C0393B7F3CDCA0849D81F84FF69B8950_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ContractWithCustomerDurationDomain" xlink:label="loc_us-gaap_ContractWithCustomerDurationDomain_C0393B7F3CDCA0849D81F84FF69B8950" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ContractWithCustomerDurationAxis_CF972923A2E199B893EEF84FA42FA6E2" xlink:to="loc_us-gaap_ContractWithCustomerDurationDomain_C0393B7F3CDCA0849D81F84FF69B8950" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShortTermContractWithCustomerMember" xlink:label="loc_us-gaap_ShortTermContractWithCustomerMember_7F8550FF16DDF432F096F85061ED6491" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerDurationDomain_C0393B7F3CDCA0849D81F84FF69B8950" xlink:to="loc_us-gaap_ShortTermContractWithCustomerMember_7F8550FF16DDF432F096F85061ED6491" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DisaggregationOfRevenueAbstract" xlink:label="loc_us-gaap_DisaggregationOfRevenueAbstract_F3A6F13A78954485B74AF8493428688F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_DC95D119BAECE4A9C4C2F8493417AEBF" xlink:to="loc_us-gaap_DisaggregationOfRevenueAbstract_F3A6F13A78954485B74AF8493428688F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax_871BFED3F007FB1470EFF8493428AC2E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueAbstract_F3A6F13A78954485B74AF8493428688F" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax_871BFED3F007FB1470EFF8493428AC2E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Revenues" xlink:label="loc_us-gaap_Revenues_37F6CB548E7D3EB8560DF8493428E185" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueAbstract_F3A6F13A78954485B74AF8493428688F" xlink:to="loc_us-gaap_Revenues_37F6CB548E7D3EB8560DF8493428E185" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RevenuePerformanceObligationAbstract" xlink:label="loc_us-gaap_RevenuePerformanceObligationAbstract_2A100CE9ED009BAB8EBCF8493428DC9E" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_DC95D119BAECE4A9C4C2F8493417AEBF" xlink:to="loc_us-gaap_RevenuePerformanceObligationAbstract_2A100CE9ED009BAB8EBCF8493428DC9E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligation" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_8C2AE72FDDDB5CC80BF4F84934280D9E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuePerformanceObligationAbstract_2A100CE9ED009BAB8EBCF8493428DC9E" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_8C2AE72FDDDB5CC80BF4F84934280D9E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetsCurrentAbstract" xlink:label="loc_us-gaap_AssetsCurrentAbstract_D7B6C51029D9762747B4F851B3A61135" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_DC95D119BAECE4A9C4C2F8493417AEBF" xlink:to="loc_us-gaap_AssetsCurrentAbstract_D7B6C51029D9762747B4F851B3A61135" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountsReceivableRelatedPartiesCurrent" xlink:label="loc_us-gaap_AccountsReceivableRelatedPartiesCurrent_48455E0A228F2C53B1FDF850E1FA5820" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_D7B6C51029D9762747B4F851B3A61135" xlink:to="loc_us-gaap_AccountsReceivableRelatedPartiesCurrent_48455E0A228F2C53B1FDF850E1FA5820" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/RevenueFromContractsWithCustomersNotes" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_744AEC8E2A95D416B4F3E37FB726F600" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_3E101B0E4C444DDD2D50E37FB725C08A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_744AEC8E2A95D416B4F3E37FB726F600" xlink:to="loc_us-gaap_StatementTable_3E101B0E4C444DDD2D50E37FB725C08A" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_9C8772771BD46C891716E37FB7261586" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_3E101B0E4C444DDD2D50E37FB725C08A" xlink:to="loc_dei_LegalEntityAxis_9C8772771BD46C891716E37FB7261586" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_50838CB98A10CA5BC9CCE37FB7266BC9_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_9C8772771BD46C891716E37FB7261586" xlink:to="loc_dei_EntityDomain_50838CB98A10CA5BC9CCE37FB7266BC9_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_50838CB98A10CA5BC9CCE37FB7266BC9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_9C8772771BD46C891716E37FB7261586" xlink:to="loc_dei_EntityDomain_50838CB98A10CA5BC9CCE37FB7266BC9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RevenueFromContractWithCustomerTextBlock" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerTextBlock_4AEC43F6B6C9C68F140BE37FB7266CDD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_744AEC8E2A95D416B4F3E37FB726F600" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerTextBlock_4AEC43F6B6C9C68F140BE37FB7266CDD" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/RevenueFromContractsWithCustomersPolicies" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.aep.com/role/RevenueFromContractsWithCustomersTables" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_C8396B154D7457B50771F89E5833B7DD" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_C6D7CC66DBBEDA599373F89E5833D0B2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_C8396B154D7457B50771F89E5833B7DD" xlink:to="loc_us-gaap_StatementTable_C6D7CC66DBBEDA599373F89E5833D0B2" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_5E0C2797B8F0A5788E14F89E5833C974" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_C6D7CC66DBBEDA599373F89E5833D0B2" xlink:to="loc_dei_LegalEntityAxis_5E0C2797B8F0A5788E14F89E5833C974" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_A50027060E60DF5F24EEF89E58330B93_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_5E0C2797B8F0A5788E14F89E5833C974" xlink:to="loc_dei_EntityDomain_A50027060E60DF5F24EEF89E58330B93_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_A50027060E60DF5F24EEF89E58330B93" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_5E0C2797B8F0A5788E14F89E5833C974" xlink:to="loc_dei_EntityDomain_A50027060E60DF5F24EEF89E58330B93" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DisaggregationOfRevenueTableTextBlock" xlink:label="loc_us-gaap_DisaggregationOfRevenueTableTextBlock_ACA2AAEF79CB9C71ACDCF89E58335FA6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_C8396B154D7457B50771F89E5833B7DD" xlink:to="loc_us-gaap_DisaggregationOfRevenueTableTextBlock_ACA2AAEF79CB9C71ACDCF89E58335FA6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTableTextBlock" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTableTextBlock_FC1F425B7514626D9135F89E58340268" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_C8396B154D7457B50771F89E5833B7DD" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTableTextBlock_FC1F425B7514626D9135F89E58340268" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AffiliatedAccountsReceivableContractswithCustomersTableTextBlock" xlink:label="loc_aep_AffiliatedAccountsReceivableContractswithCustomersTableTextBlock_582B7D82C820FFA3180AF89E583422B3" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_C8396B154D7457B50771F89E5833B7DD" xlink:to="loc_aep_AffiliatedAccountsReceivableContractswithCustomersTableTextBlock_582B7D82C820FFA3180AF89E583422B3" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/SignificantAccountingMatters" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_4C6C1C3FB4C42BD6E088F3B36300A4DC" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_434866E0FCF60C23B442F3B3630098D4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_4C6C1C3FB4C42BD6E088F3B36300A4DC" xlink:to="loc_us-gaap_StatementTable_434866E0FCF60C23B442F3B3630098D4" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_006D905F34E38DF3296FF3B36300940C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_434866E0FCF60C23B442F3B3630098D4" xlink:to="loc_dei_LegalEntityAxis_006D905F34E38DF3296FF3B36300940C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_A541249513E7B1CE9180F3B36300AC0F_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_006D905F34E38DF3296FF3B36300940C" xlink:to="loc_dei_EntityDomain_A541249513E7B1CE9180F3B36300AC0F_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_A541249513E7B1CE9180F3B36300AC0F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_006D905F34E38DF3296FF3B36300940C" xlink:to="loc_dei_EntityDomain_A541249513E7B1CE9180F3B36300AC0F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SignificantAccountingPoliciesTextBlock" xlink:label="loc_us-gaap_SignificantAccountingPoliciesTextBlock_B0BA40E7C6B251B2D5B2F3B363006BC2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_4C6C1C3FB4C42BD6E088F3B36300A4DC" xlink:to="loc_us-gaap_SignificantAccountingPoliciesTextBlock_B0BA40E7C6B251B2D5B2F3B363006BC2" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/SignificantAccountingMattersDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_327D83E387673AF4B243D524C4EA6E32" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_68024C88FDBD2E3E4572D524C4E870BB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_327D83E387673AF4B243D524C4EA6E32" xlink:to="loc_us-gaap_StatementTable_68024C88FDBD2E3E4572D524C4E870BB" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_BD8AA1D71899821A3616D524C4E9477B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_68024C88FDBD2E3E4572D524C4E870BB" xlink:to="loc_dei_LegalEntityAxis_BD8AA1D71899821A3616D524C4E9477B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_FF0D14CAE8001C22E515D524C4E9975E_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_BD8AA1D71899821A3616D524C4E9477B" xlink:to="loc_dei_EntityDomain_FF0D14CAE8001C22E515D524C4E9975E_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_FF0D14CAE8001C22E515D524C4E9975E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_BD8AA1D71899821A3616D524C4E9477B" xlink:to="loc_dei_EntityDomain_FF0D14CAE8001C22E515D524C4E9975E" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPTexasInc.Member" xlink:label="loc_aep_AEPTexasInc.Member_ECD5FC6830D9450FFD16D524C4EAD3BA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_FF0D14CAE8001C22E515D524C4E9975E" xlink:to="loc_aep_AEPTexasInc.Member_ECD5FC6830D9450FFD16D524C4EAD3BA" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AppalachianPowerCoMember" xlink:label="loc_aep_AppalachianPowerCoMember_B12F702D16C361855250D5257E7F7965" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_FF0D14CAE8001C22E515D524C4E9975E" xlink:to="loc_aep_AppalachianPowerCoMember_B12F702D16C361855250D5257E7F7965" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OhioPowerCoMember" xlink:label="loc_aep_OhioPowerCoMember_7C8DE81A33ECAA475D11D5262DCDE7A7" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_FF0D14CAE8001C22E515D524C4E9975E" xlink:to="loc_aep_OhioPowerCoMember_7C8DE81A33ECAA475D11D5262DCDE7A7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_52F12C65EC308AE911C3D524C4EA8E80" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_68024C88FDBD2E3E4572D524C4E870BB" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_52F12C65EC308AE911C3D524C4EA8E80" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_E27CD1105B248FBF816BD524C4EA3655_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_52F12C65EC308AE911C3D524C4EA8E80" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_E27CD1105B248FBF816BD524C4EA3655_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_E27CD1105B248FBF816BD524C4EA3655" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_52F12C65EC308AE911C3D524C4EA8E80" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_E27CD1105B248FBF816BD524C4EA3655" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_RestrictedStockUnitsandPerformanceShareUnitsMember" xlink:label="loc_aep_RestrictedStockUnitsandPerformanceShareUnitsMember_F989C8E7F26067D1C071D524C4EA7D9B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_E27CD1105B248FBF816BD524C4EA3655" xlink:to="loc_aep_RestrictedStockUnitsandPerformanceShareUnitsMember_F989C8E7F26067D1C071D524C4EA7D9B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EarningsPerShareAbstract" xlink:label="loc_us-gaap_EarningsPerShareAbstract_ABA344303C81B53ED29CD524C4EAE9CB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_327D83E387673AF4B243D524C4EA6E32" xlink:to="loc_us-gaap_EarningsPerShareAbstract_ABA344303C81B53ED29CD524C4EAE9CB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract_0D76564A4A68446A09FBD524C4EA8300" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_ABA344303C81B53ED29CD524C4EAE9CB" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract_0D76564A4A68446A09FBD524C4EA8300" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_DB637A6BBCFFC844296DD524C4EBF647" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract_0D76564A4A68446A09FBD524C4EA8300" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_DB637A6BBCFFC844296DD524C4EBF647" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_EC0DACABA58FEDE729C5D524C4EB527A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_ABA344303C81B53ED29CD524C4EAE9CB" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_EC0DACABA58FEDE729C5D524C4EB527A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsPerBasicShare" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsPerBasicShare_97FBB343250FFAC4C819D524C4EBE73B" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_ABA344303C81B53ED29CD524C4EAE9CB" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsPerBasicShare_97FBB343250FFAC4C819D524C4EBE73B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract" xlink:label="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_6A5445DB7FCDD3F193A7D524C4EB88A0" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_ABA344303C81B53ED29CD524C4EAE9CB" xlink:to="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_6A5445DB7FCDD3F193A7D524C4EB88A0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_BD914655091471CA137FD524C4EBB068" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_6A5445DB7FCDD3F193A7D524C4EB88A0" xlink:to="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_BD914655091471CA137FD524C4EBB068" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_DilutiveSecurities1" xlink:label="loc_aep_DilutiveSecurities1_B700CCA9752FE48038A2D524C4EBC296" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_6A5445DB7FCDD3F193A7D524C4EB88A0" xlink:to="loc_aep_DilutiveSecurities1_B700CCA9752FE48038A2D524C4EBC296" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_93D51FDF637CE86EC121D524C4EB07EF" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_6A5445DB7FCDD3F193A7D524C4EB88A0" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_93D51FDF637CE86EC121D524C4EB07EF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare_F8F008DB09C6F78CF86ED524C4EB812F" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_6A5445DB7FCDD3F193A7D524C4EB88A0" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare_F8F008DB09C6F78CF86ED524C4EB812F" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_OrganizationAndSummaryOfSignificantAccountingPoliciesTextualsAbstract" xlink:label="loc_aep_OrganizationAndSummaryOfSignificantAccountingPoliciesTextualsAbstract_C32E4010166FD107FA6FD524C4EB6FC0" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_327D83E387673AF4B243D524C4EA6E32" xlink:to="loc_aep_OrganizationAndSummaryOfSignificantAccountingPoliciesTextualsAbstract_C32E4010166FD107FA6FD524C4EB6FC0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_6FE88524DCBFC450CB09D524C4EB69B2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_OrganizationAndSummaryOfSignificantAccountingPoliciesTextualsAbstract_C32E4010166FD107FA6FD524C4EB6FC0" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_6FE88524DCBFC450CB09D524C4EB69B2" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_CashCashEquivalentsandRestrictedCashAbstract" xlink:label="loc_aep_CashCashEquivalentsandRestrictedCashAbstract_F572937E53DE8D51AEC4D524C4EB2BE9" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_327D83E387673AF4B243D524C4EA6E32" xlink:to="loc_aep_CashCashEquivalentsandRestrictedCashAbstract_F572937E53DE8D51AEC4D524C4EB2BE9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_76DECB04E310A91C873AD524C4EB95DE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CashCashEquivalentsandRestrictedCashAbstract_F572937E53DE8D51AEC4D524C4EB2BE9" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_76DECB04E310A91C873AD524C4EB95DE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue_EC9EC50CD27A357E7B0BD524C4EB682A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CashCashEquivalentsandRestrictedCashAbstract_F572937E53DE8D51AEC4D524C4EB2BE9" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue_EC9EC50CD27A357E7B0BD524C4EB682A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_533D9F49A86F0E40DCB6D524C4EB95BD" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CashCashEquivalentsandRestrictedCashAbstract_F572937E53DE8D51AEC4D524C4EB2BE9" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_533D9F49A86F0E40DCB6D524C4EB95BD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_D3C5B1BDED74A4FEFA44D524C4EBC98F" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_CashCashEquivalentsandRestrictedCashAbstract_F572937E53DE8D51AEC4D524C4EB2BE9" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_D3C5B1BDED74A4FEFA44D524C4EBC98F" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/SignificantAccountingMattersPolicies" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_39AAC9E54E473E4546FDFD0AECE8B93C" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_C2FED7DD45750056F8F9FD0AECE80279" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_39AAC9E54E473E4546FDFD0AECE8B93C" xlink:to="loc_us-gaap_StatementTable_C2FED7DD45750056F8F9FD0AECE80279" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_FFAECDA62B0EDAEBFA38FD0AECE82A4A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_C2FED7DD45750056F8F9FD0AECE80279" xlink:to="loc_dei_LegalEntityAxis_FFAECDA62B0EDAEBFA38FD0AECE82A4A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_3A6B3B48F88F71130C58FD0AECE8BE1D_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_FFAECDA62B0EDAEBFA38FD0AECE82A4A" xlink:to="loc_dei_EntityDomain_3A6B3B48F88F71130C58FD0AECE8BE1D_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_3A6B3B48F88F71130C58FD0AECE8BE1D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_FFAECDA62B0EDAEBFA38FD0AECE82A4A" xlink:to="loc_dei_EntityDomain_3A6B3B48F88F71130C58FD0AECE8BE1D" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_BasisOfAccountingTextBlock" xlink:label="loc_aep_BasisOfAccountingTextBlock_8A934CCFA8180D9109B9FD0AECE87AD9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_39AAC9E54E473E4546FDFD0AECE8B93C" xlink:to="loc_aep_BasisOfAccountingTextBlock_8A934CCFA8180D9109B9FD0AECE87AD9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EarningsPerSharePolicyTextBlock" xlink:label="loc_us-gaap_EarningsPerSharePolicyTextBlock_9568C33E5D4D54059683FD0AECE8FF17" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_39AAC9E54E473E4546FDFD0AECE8B93C" xlink:to="loc_us-gaap_EarningsPerSharePolicyTextBlock_9568C33E5D4D54059683FD0AECE8FF17" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/SignificantAccountingMattersTables" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_DF5E61C8B319E27F897BD4CA46C26C65" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_3A0B4BBF78756AFA4817D4CA46C1974A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_DF5E61C8B319E27F897BD4CA46C26C65" xlink:to="loc_us-gaap_StatementTable_3A0B4BBF78756AFA4817D4CA46C1974A" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_8A220B6A6368AC070563D4CA46C12B2F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_3A0B4BBF78756AFA4817D4CA46C1974A" xlink:to="loc_dei_LegalEntityAxis_8A220B6A6368AC070563D4CA46C12B2F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_DFE1F09C1DEF4356F3D4D4CA46C203DD_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_8A220B6A6368AC070563D4CA46C12B2F" xlink:to="loc_dei_EntityDomain_DFE1F09C1DEF4356F3D4D4CA46C203DD_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_DFE1F09C1DEF4356F3D4D4CA46C203DD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_8A220B6A6368AC070563D4CA46C12B2F" xlink:to="loc_dei_EntityDomain_DFE1F09C1DEF4356F3D4D4CA46C203DD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EarningsPerShareTextBlock" xlink:label="loc_us-gaap_EarningsPerShareTextBlock_5127D86D7006E4538C81D4CA46C226EB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_DF5E61C8B319E27F897BD4CA46C26C65" xlink:to="loc_us-gaap_EarningsPerShareTextBlock_5127D86D7006E4538C81D4CA46C226EB" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ReconciliationofCashCashEquivalentsandRestrictedCashTableTextBlock" xlink:label="loc_aep_ReconciliationofCashCashEquivalentsandRestrictedCashTableTextBlock_E445B453CAD6107D9731D4CF2820CF8E" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_DF5E61C8B319E27F897BD4CA46C26C65" xlink:to="loc_aep_ReconciliationofCashCashEquivalentsandRestrictedCashTableTextBlock_E445B453CAD6107D9731D4CF2820CF8E" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/VariableInterestEntitiesDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_E2A7569C935C03533A84F415FFAB70FF" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_1CBD6AC7C0A668817FDFF415FFAADF42" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_E2A7569C935C03533A84F415FFAB70FF" xlink:to="loc_us-gaap_StatementTable_1CBD6AC7C0A668817FDFF415FFAADF42" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BalanceSheetLocationAxis" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_7747D86B255282D99F9AF415FFAA595B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_1CBD6AC7C0A668817FDFF415FFAADF42" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_7747D86B255282D99F9AF415FFAA595B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_85B526DF611245511F9DF415FFAADA36_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_7747D86B255282D99F9AF415FFAA595B" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_85B526DF611245511F9DF415FFAADA36_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_85B526DF611245511F9DF415FFAADA36" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_7747D86B255282D99F9AF415FFAA595B" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_85B526DF611245511F9DF415FFAADA36" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_CurrentAssetsMember" xlink:label="loc_aep_CurrentAssetsMember_6A0FE9FCB0400B78E9D8F415FFAA2462" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_85B526DF611245511F9DF415FFAADA36" xlink:to="loc_aep_CurrentAssetsMember_6A0FE9FCB0400B78E9D8F415FFAA2462" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_NetPropertyPlantAndEquipmentMember" xlink:label="loc_aep_NetPropertyPlantAndEquipmentMember_01DC6D4543E897F7333BF415FFAA3450" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_85B526DF611245511F9DF415FFAADA36" xlink:to="loc_aep_NetPropertyPlantAndEquipmentMember_01DC6D4543E897F7333BF415FFAA3450" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherNoncurrentAssetsMember" xlink:label="loc_us-gaap_OtherNoncurrentAssetsMember_18C15E6472EB93D89BDCF415FFAA4D1A" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_85B526DF611245511F9DF415FFAADA36" xlink:to="loc_us-gaap_OtherNoncurrentAssetsMember_18C15E6472EB93D89BDCF415FFAA4D1A" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_TotalAssetsMember" xlink:label="loc_aep_TotalAssetsMember_C476F55A0711A833FDD0F415FFAA2639" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_85B526DF611245511F9DF415FFAADA36" xlink:to="loc_aep_TotalAssetsMember_C476F55A0711A833FDD0F415FFAA2639" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_CurrentLiabilitiesMember" xlink:label="loc_aep_CurrentLiabilitiesMember_89D5B5EC92ED5BF1ADF0F415FFAAC436" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_85B526DF611245511F9DF415FFAADA36" xlink:to="loc_aep_CurrentLiabilitiesMember_89D5B5EC92ED5BF1ADF0F415FFAAC436" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_NoncurrentLiabilitiesMember" xlink:label="loc_aep_NoncurrentLiabilitiesMember_A820CA68B43AE671A036F415FFAA6F7F" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_85B526DF611245511F9DF415FFAADA36" xlink:to="loc_aep_NoncurrentLiabilitiesMember_A820CA68B43AE671A036F415FFAA6F7F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityMember" xlink:label="loc_us-gaap_EquityMember_F396FF86489572B5BB16F415FFAA26D2" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_85B526DF611245511F9DF415FFAADA36" xlink:to="loc_us-gaap_EquityMember_F396FF86489572B5BB16F415FFAA26D2" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_TotalLiabilitiesAndEquityMember" xlink:label="loc_aep_TotalLiabilitiesAndEquityMember_21806E5E8D0DE675F488F415FFAAC59B" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_85B526DF611245511F9DF415FFAADA36" xlink:to="loc_aep_TotalLiabilitiesAndEquityMember_21806E5E8D0DE675F488F415FFAAC59B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis" xlink:label="loc_us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis_C7955A010D4858D9E0D5F415FFAADD20" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_1CBD6AC7C0A668817FDFF415FFAADF42" xlink:to="loc_us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis_C7955A010D4858D9E0D5F415FFAADD20" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassificationOfVariableInterestEntityDomain" xlink:label="loc_us-gaap_ClassificationOfVariableInterestEntityDomain_CBDA45AE204C77519480F415FFAB75E1_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis_C7955A010D4858D9E0D5F415FFAADD20" xlink:to="loc_us-gaap_ClassificationOfVariableInterestEntityDomain_CBDA45AE204C77519480F415FFAB75E1_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassificationOfVariableInterestEntityDomain" xlink:label="loc_us-gaap_ClassificationOfVariableInterestEntityDomain_CBDA45AE204C77519480F415FFAB75E1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis_C7955A010D4858D9E0D5F415FFAADD20" xlink:to="loc_us-gaap_ClassificationOfVariableInterestEntityDomain_CBDA45AE204C77519480F415FFAB75E1" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_TrentandDesertSkyWindFarmsMember" xlink:label="loc_aep_TrentandDesertSkyWindFarmsMember_98E1B5FC75610E74F1FFF415FFABA5A7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassificationOfVariableInterestEntityDomain_CBDA45AE204C77519480F415FFAB75E1" xlink:to="loc_aep_TrentandDesertSkyWindFarmsMember_98E1B5FC75610E74F1FFF415FFABA5A7" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_NonAffiliateContributionMember" xlink:label="loc_aep_NonAffiliateContributionMember_72F5A885CA8E310CBD89F415FFAB0474" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassificationOfVariableInterestEntityDomain_CBDA45AE204C77519480F415FFAB75E1" xlink:to="loc_aep_NonAffiliateContributionMember_72F5A885CA8E310CBD89F415FFAB0474" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssetsAndLiabilitiesAbstract" xlink:label="loc_us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssetsAndLiabilitiesAbstract_60B917A4A4AC9C746C8AF415FFAB315D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E2A7569C935C03533A84F415FFAB70FF" xlink:to="loc_us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssetsAndLiabilitiesAbstract_60B917A4A4AC9C746C8AF415FFAB315D" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_VariableInterestCarryingAmountAssetsAbstract" xlink:label="loc_aep_VariableInterestCarryingAmountAssetsAbstract_531414B9AACF345A827FF415FFABCD00" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssetsAndLiabilitiesAbstract_60B917A4A4AC9C746C8AF415FFAB315D" xlink:to="loc_aep_VariableInterestCarryingAmountAssetsAbstract_531414B9AACF345A827FF415FFABCD00" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets" xlink:label="loc_us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets_925D48A28998D35D9075F415FFAB8D99" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_VariableInterestCarryingAmountAssetsAbstract_531414B9AACF345A827FF415FFABCD00" xlink:to="loc_us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets_925D48A28998D35D9075F415FFAB8D99" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_VariableInterestCarryingAmountLiabilitiesAndEquityAbstract" xlink:label="loc_aep_VariableInterestCarryingAmountLiabilitiesAndEquityAbstract_799196FD27D178595C9CF415FFAB4003" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssetsAndLiabilitiesAbstract_60B917A4A4AC9C746C8AF415FFAB315D" xlink:to="loc_aep_VariableInterestCarryingAmountLiabilitiesAndEquityAbstract_799196FD27D178595C9CF415FFAB4003" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_VariableInterestCarryingAmountLiabilitiesAndEquity" xlink:label="loc_aep_VariableInterestCarryingAmountLiabilitiesAndEquity_35ECB0A602F143494507F415FFABFE0F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_VariableInterestCarryingAmountLiabilitiesAndEquityAbstract_799196FD27D178595C9CF415FFAB4003" xlink:to="loc_aep_VariableInterestCarryingAmountLiabilitiesAndEquity_35ECB0A602F143494507F415FFABFE0F" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_VariableInterestEntitiesTextualsAbstract" xlink:label="loc_aep_VariableInterestEntitiesTextualsAbstract_E79FD90CC5E236E2D285F415FFAB0D65" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_E2A7569C935C03533A84F415FFAB70FF" xlink:to="loc_aep_VariableInterestEntitiesTextualsAbstract_E79FD90CC5E236E2D285F415FFAB0D65" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_WindGenerationMWs" xlink:label="loc_aep_WindGenerationMWs_6B78811CFD51FD05D1DEF415FFABA896" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_VariableInterestEntitiesTextualsAbstract_E79FD90CC5E236E2D285F415FFAB0D65" xlink:to="loc_aep_WindGenerationMWs_6B78811CFD51FD05D1DEF415FFABA896" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_NonAffiliateInterest" xlink:label="loc_aep_NonAffiliateInterest_3A41635F643F409A7C1EF415FFAB04EC" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_VariableInterestEntitiesTextualsAbstract_E79FD90CC5E236E2D285F415FFAB0D65" xlink:to="loc_aep_NonAffiliateInterest_3A41635F643F409A7C1EF415FFAB04EC" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_AEPOwnershipinLLCs" xlink:label="loc_aep_AEPOwnershipinLLCs_DCEBD7E4179E312E451BF415FFABF60A" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_VariableInterestEntitiesTextualsAbstract_E79FD90CC5E236E2D285F415FFAB0D65" xlink:to="loc_aep_AEPOwnershipinLLCs_DCEBD7E4179E312E451BF415FFABF60A" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_DesertSkyandTrentPPAPeriod" xlink:label="loc_aep_DesertSkyandTrentPPAPeriod_6A635E54E953BDE1FBBCF415FFAB6EFE" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_VariableInterestEntitiesTextualsAbstract_E79FD90CC5E236E2D285F415FFAB0D65" xlink:to="loc_aep_DesertSkyandTrentPPAPeriod_6A635E54E953BDE1FBBCF415FFAB6EFE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount" xlink:label="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_823A38E4F43725C6C01DF415FFAC751B" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_aep_VariableInterestEntitiesTextualsAbstract_E79FD90CC5E236E2D285F415FFAB0D65" xlink:to="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_823A38E4F43725C6C01DF415FFAC751B" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/VariableInterestEntitiesNotes" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_15999CD4AC9EE8B79DE5F33FFCF8C686" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_C17B39DE3BB1EAABCC24F33FFCF80CF8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_15999CD4AC9EE8B79DE5F33FFCF8C686" xlink:to="loc_us-gaap_StatementTable_C17B39DE3BB1EAABCC24F33FFCF80CF8" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_0EA5789712E8A0F9996FF33FFCF81BAE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_C17B39DE3BB1EAABCC24F33FFCF80CF8" xlink:to="loc_dei_LegalEntityAxis_0EA5789712E8A0F9996FF33FFCF81BAE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_1D2628B2EFB7CF505E7FF33FFCF8E6F5_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_0EA5789712E8A0F9996FF33FFCF81BAE" xlink:to="loc_dei_EntityDomain_1D2628B2EFB7CF505E7FF33FFCF8E6F5_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_1D2628B2EFB7CF505E7FF33FFCF8E6F5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_0EA5789712E8A0F9996FF33FFCF81BAE" xlink:to="loc_dei_EntityDomain_1D2628B2EFB7CF505E7FF33FFCF8E6F5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableInterestEntityDisclosureTextBlock" xlink:label="loc_us-gaap_VariableInterestEntityDisclosureTextBlock_7E824B8AF54948B706BDF33FFCF8C9E5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_15999CD4AC9EE8B79DE5F33FFCF8C686" xlink:to="loc_us-gaap_VariableInterestEntityDisclosureTextBlock_7E824B8AF54948B706BDF33FFCF8C9E5" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/VariableInterestEntitiesPolicies" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_3DA9429B452FE29E0AF4F33FFA1E4D64" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_A1BD9F120F3B7F54EB6BF33FFA1ED122" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_3DA9429B452FE29E0AF4F33FFA1E4D64" xlink:to="loc_us-gaap_StatementTable_A1BD9F120F3B7F54EB6BF33FFA1ED122" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_1193EEDC843A60923B46F33FFA1E1BC3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_A1BD9F120F3B7F54EB6BF33FFA1ED122" xlink:to="loc_dei_LegalEntityAxis_1193EEDC843A60923B46F33FFA1E1BC3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_5D9831C4D3341A31940EF33FFA1E38D8_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_1193EEDC843A60923B46F33FFA1E1BC3" xlink:to="loc_dei_EntityDomain_5D9831C4D3341A31940EF33FFA1E38D8_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_5D9831C4D3341A31940EF33FFA1E38D8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_1193EEDC843A60923B46F33FFA1E1BC3" xlink:to="loc_dei_EntityDomain_5D9831C4D3341A31940EF33FFA1E38D8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidationVariableInterestEntityPolicy" xlink:label="loc_us-gaap_ConsolidationVariableInterestEntityPolicy_5757BEC22573BA59302FF33FFA1EEA49" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3DA9429B452FE29E0AF4F33FFA1E4D64" xlink:to="loc_us-gaap_ConsolidationVariableInterestEntityPolicy_5757BEC22573BA59302FF33FFA1EEA49" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.aep.com/role/VariableInterestEntitiesTables" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_B8E4CD2BD0C9844F3B07F33B136B55D9" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_BCDEE32BAA88CD1EE47BF33B136BEC2C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_B8E4CD2BD0C9844F3B07F33B136B55D9" xlink:to="loc_us-gaap_StatementTable_BCDEE32BAA88CD1EE47BF33B136BEC2C" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis" xlink:label="loc_us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis_4CC9E928FEA5DB22731AF3C87C5B9076" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_BCDEE32BAA88CD1EE47BF33B136BEC2C" xlink:to="loc_us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis_4CC9E928FEA5DB22731AF3C87C5B9076" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassificationOfVariableInterestEntityDomain" xlink:label="loc_us-gaap_ClassificationOfVariableInterestEntityDomain_F4875020327962CC5A0DF3C87C5B4602_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis_4CC9E928FEA5DB22731AF3C87C5B9076" xlink:to="loc_us-gaap_ClassificationOfVariableInterestEntityDomain_F4875020327962CC5A0DF3C87C5B4602_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassificationOfVariableInterestEntityDomain" xlink:label="loc_us-gaap_ClassificationOfVariableInterestEntityDomain_F4875020327962CC5A0DF3C87C5B4602" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis_4CC9E928FEA5DB22731AF3C87C5B9076" xlink:to="loc_us-gaap_ClassificationOfVariableInterestEntityDomain_F4875020327962CC5A0DF3C87C5B4602" xlink:type="arc" />
    <link:loc xlink:href="aep-20180331.xsd#aep_ConsolidatedAssetsAndLiabilitiesOfVariableInterestEntitiesTableTextBlock" xlink:label="loc_aep_ConsolidatedAssetsAndLiabilitiesOfVariableInterestEntitiesTableTextBlock_6C2C2DB5F49FD0A511ABF33B136B5134" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_B8E4CD2BD0C9844F3B07F33B136B55D9" xlink:to="loc_aep_ConsolidatedAssetsAndLiabilitiesOfVariableInterestEntitiesTableTextBlock_6C2C2DB5F49FD0A511ABF33B136B5134" xlink:type="arc" />
  </link:definitionLink>
</link:linkbase>
