<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019c1ff6-d4e1-7de1-b1f5-027f91df6c7d,g:1a3fa854-ad24-4ff5-b142-0192914aadee-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.airproducts.com/role/Cover" xlink:type="simple" xlink:href="apd-20260331.xsd#Cover"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/Cover" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_019c1ff6-d7d5-7688-aca7-4b7540f5f32e" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_EntitiesTable_019c1ff6-d7d5-7688-aca7-4b7540f5f32e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019c1ff6-d7d5-70f4-b429-c73148534424" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_019c1ff6-d7d5-7688-aca7-4b7540f5f32e" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019c1ff6-d7d5-70f4-b429-c73148534424" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019c1ff6-d7d5-70f4-b429-c73148534424_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019c1ff6-d7d5-70f4-b429-c73148534424" xlink:to="loc_us-gaap_ClassOfStockDomain_019c1ff6-d7d5-70f4-b429-c73148534424_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019c1ff6-d7d5-7eb8-b63e-4b0ace5614b8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019c1ff6-d7d5-70f4-b429-c73148534424" xlink:to="loc_us-gaap_ClassOfStockDomain_019c1ff6-d7d5-7eb8-b63e-4b0ace5614b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019c1ff6-d7d5-7005-b2ca-4cd76275a8c1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019c1ff6-d7d5-7eb8-b63e-4b0ace5614b8" xlink:to="loc_us-gaap_CommonClassAMember_019c1ff6-d7d5-7005-b2ca-4cd76275a8c1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_A0500EuroNotesDue2028Member_019c1ff6-d7d5-7518-b6b8-7c388049a941" xlink:href="apd-20260331.xsd#apd_A0500EuroNotesDue2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019c1ff6-d7d5-7eb8-b63e-4b0ace5614b8" xlink:to="loc_apd_A0500EuroNotesDue2028Member_019c1ff6-d7d5-7518-b6b8-7c388049a941" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_A2.950NotesDue2031Member_019c1ff6-d7d5-70c9-abd4-fe7dd8af5b40" xlink:href="apd-20260331.xsd#apd_A2.950NotesDue2031Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019c1ff6-d7d5-7eb8-b63e-4b0ace5614b8" xlink:to="loc_apd_A2.950NotesDue2031Member_019c1ff6-d7d5-70c9-abd4-fe7dd8af5b40" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_A0800EuroNotesDue2032Member_019c1ff6-d7d5-7c24-a2ce-8237123610b7" xlink:href="apd-20260331.xsd#apd_A0800EuroNotesDue2032Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019c1ff6-d7d5-7eb8-b63e-4b0ace5614b8" xlink:to="loc_apd_A0800EuroNotesDue2032Member_019c1ff6-d7d5-7c24-a2ce-8237123610b7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_A3.250EuroNotesDue2032Member_019c1ff6-d7d5-719c-b598-fd4cc582cf58" xlink:href="apd-20260331.xsd#apd_A3.250EuroNotesDue2032Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019c1ff6-d7d5-7eb8-b63e-4b0ace5614b8" xlink:to="loc_apd_A3.250EuroNotesDue2032Member_019c1ff6-d7d5-719c-b598-fd4cc582cf58" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_A4000EuroNotesDue2035Member_019c1ff6-d7d5-711e-8c10-fbd91bec0de9" xlink:href="apd-20260331.xsd#apd_A4000EuroNotesDue2035Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019c1ff6-d7d5-7eb8-b63e-4b0ace5614b8" xlink:to="loc_apd_A4000EuroNotesDue2035Member_019c1ff6-d7d5-711e-8c10-fbd91bec0de9" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_A3.450NotesDue2037Member_019c1ff6-d7d5-7bed-8daa-dc66bde2178d" xlink:href="apd-20260331.xsd#apd_A3.450NotesDue2037Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019c1ff6-d7d5-7eb8-b63e-4b0ace5614b8" xlink:to="loc_apd_A3.450NotesDue2037Member_019c1ff6-d7d5-7bed-8daa-dc66bde2178d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_019c1ff6-d7d5-708c-96aa-b056a5965c40" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_DocumentType_019c1ff6-d7d5-708c-96aa-b056a5965c40" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentQuarterlyReport_019c1ff6-d7d5-7e7e-972a-b46cd48ec009" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentQuarterlyReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_DocumentQuarterlyReport_019c1ff6-d7d5-7e7e-972a-b46cd48ec009" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_019c1ff6-d7d5-7c9e-9b9c-19a39db12993" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_DocumentPeriodEndDate_019c1ff6-d7d5-7c9e-9b9c-19a39db12993" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_019c1ff6-d7d5-781b-a1ff-0adb24461895" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_DocumentTransitionReport_019c1ff6-d7d5-781b-a1ff-0adb24461895" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_019c1ff6-d7d5-7a1e-99dd-21d555183e9c" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_EntityFileNumber_019c1ff6-d7d5-7a1e-99dd-21d555183e9c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_019c1ff6-d7d5-7876-8c68-bdac9d9f288f" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_EntityRegistrantName_019c1ff6-d7d5-7876-8c68-bdac9d9f288f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_019c1ff6-d7d5-7247-9360-67d9c4293b87" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_EntityIncorporationStateCountryCode_019c1ff6-d7d5-7247-9360-67d9c4293b87" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_019c1ff6-d7d5-7430-b32d-b8469896c2c0" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_EntityTaxIdentificationNumber_019c1ff6-d7d5-7430-b32d-b8469896c2c0" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_019c1ff6-d7d5-71fc-b28d-fdc5e66743ce" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_EntityAddressAddressLine1_019c1ff6-d7d5-71fc-b28d-fdc5e66743ce" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_019c1ff6-d7d5-798b-980e-f41e0776c6ed" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_EntityAddressCityOrTown_019c1ff6-d7d5-798b-980e-f41e0776c6ed" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_019c1ff6-d7d5-7c3b-a294-814caa28eedd" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_EntityAddressStateOrProvince_019c1ff6-d7d5-7c3b-a294-814caa28eedd" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_019c1ff6-d7d5-73f3-9539-2f004feaef0c" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_EntityAddressPostalZipCode_019c1ff6-d7d5-73f3-9539-2f004feaef0c" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_019c1ff6-d7d5-70f5-95a0-88258a399421" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_CityAreaCode_019c1ff6-d7d5-70f5-95a0-88258a399421" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_019c1ff6-d7d5-79d0-92a4-d6a09a0fefb8" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_LocalPhoneNumber_019c1ff6-d7d5-79d0-92a4-d6a09a0fefb8" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_019c1ff6-d7d5-75f8-b16e-73a983276cd0" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_Security12bTitle_019c1ff6-d7d5-75f8-b16e-73a983276cd0" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_019c1ff6-d7d5-73fa-a9fe-46955edcbcda" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_TradingSymbol_019c1ff6-d7d5-73fa-a9fe-46955edcbcda" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_019c1ff6-d7d5-794d-ab79-9353decc5afb" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_SecurityExchangeName_019c1ff6-d7d5-794d-ab79-9353decc5afb" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_019c1ff6-d7d5-703d-839e-6419232788d9" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_EntityCurrentReportingStatus_019c1ff6-d7d5-703d-839e-6419232788d9" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_019c1ff6-d7d5-7c40-9135-956cd27e0da0" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_EntityInteractiveDataCurrent_019c1ff6-d7d5-7c40-9135-956cd27e0da0" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_019c1ff6-d7d5-788d-8ccd-712b82bbd35a" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_EntityFilerCategory_019c1ff6-d7d5-788d-8ccd-712b82bbd35a" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_019c1ff6-d7d5-7295-8dd1-74f52dab9ef1" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntitySmallBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_EntitySmallBusiness_019c1ff6-d7d5-7295-8dd1-74f52dab9ef1" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_019c1ff6-d7d5-7f09-b264-99e82340e50c" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_EntityEmergingGrowthCompany_019c1ff6-d7d5-7f09-b264-99e82340e50c" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_019c1ff6-d7d5-7921-ad42-1a5a9f759e90" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_EntityShellCompany_019c1ff6-d7d5-7921-ad42-1a5a9f759e90" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_019c1ff6-d7d5-7644-bedd-699d92fde24f" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_019c1ff6-d7d5-7644-bedd-699d92fde24f" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_019c1ff6-d7d5-72a4-ad85-ad4dacb8f60e" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_EntityCentralIndexKey_019c1ff6-d7d5-72a4-ad85-ad4dacb8f60e" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_019c1ff6-d7d5-7ba0-8eae-39623d2f4ab0" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_CurrentFiscalYearEndDate_019c1ff6-d7d5-7ba0-8eae-39623d2f4ab0" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_019c1ff6-d7d5-70cd-b9c8-31f6204e6a69" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_DocumentFiscalYearFocus_019c1ff6-d7d5-70cd-b9c8-31f6204e6a69" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_019c1ff6-d7d5-78e0-876f-464be48b8103" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_DocumentFiscalPeriodFocus_019c1ff6-d7d5-78e0-876f-464be48b8103" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_019c1ff6-d7d5-70c3-9a59-147ff50291db" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c1ff6-d7d5-76ad-a5f4-31b6fbe6765b" xlink:to="loc_dei_AmendmentFlag_019c1ff6-d7d5-70c3-9a59-147ff50291db" xlink:type="arc" order="28"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/ConsolidatedBalanceSheetsUnaudited" xlink:type="simple" xlink:href="apd-20260331.xsd#ConsolidatedBalanceSheetsUnaudited"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/ConsolidatedBalanceSheetsUnaudited" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019c1ff6-d7d5-74da-980f-a7e78391cc84" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019c1ff6-d7d5-7380-836c-c421acf4f627" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019c1ff6-d7d5-74da-980f-a7e78391cc84" xlink:to="loc_us-gaap_StatementTable_019c1ff6-d7d5-7380-836c-c421acf4f627" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019c1ff6-d7d5-7bbe-9373-401fe2d0f2ac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019c1ff6-d7d5-7380-836c-c421acf4f627" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019c1ff6-d7d5-7bbe-9373-401fe2d0f2ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019c1ff6-d7d5-7bbe-9373-401fe2d0f2ac_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019c1ff6-d7d5-7bbe-9373-401fe2d0f2ac" xlink:to="loc_us-gaap_RelatedPartyDomain_019c1ff6-d7d5-7bbe-9373-401fe2d0f2ac_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019c1ff6-d7d5-7e49-92d1-4257847bcd9b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019c1ff6-d7d5-7bbe-9373-401fe2d0f2ac" xlink:to="loc_us-gaap_RelatedPartyDomain_019c1ff6-d7d5-7e49-92d1-4257847bcd9b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonrelatedPartyMember_019c1ff6-d7d5-778a-bebd-d4a3776263c6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NonrelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019c1ff6-d7d5-7e49-92d1-4257847bcd9b" xlink:to="loc_us-gaap_NonrelatedPartyMember_019c1ff6-d7d5-778a-bebd-d4a3776263c6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019c1ff6-d7d5-7e11-ae1d-70970f3820fd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019c1ff6-d7d5-7e49-92d1-4257847bcd9b" xlink:to="loc_us-gaap_RelatedPartyMember_019c1ff6-d7d5-7e11-ae1d-70970f3820fd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_019c1ff6-d7d5-7f64-b820-2b59c3b80b11" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019c1ff6-d7d5-74da-980f-a7e78391cc84" xlink:to="loc_us-gaap_AssetsAbstract_019c1ff6-d7d5-7f64-b820-2b59c3b80b11" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrentAbstract_019c1ff6-d7d5-7a53-974f-2f93f217fea2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019c1ff6-d7d5-7f64-b820-2b59c3b80b11" xlink:to="loc_us-gaap_AssetsCurrentAbstract_019c1ff6-d7d5-7a53-974f-2f93f217fea2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019c1ff6-d7d5-7e80-85ce-01cbf853e7e8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019c1ff6-d7d5-7a53-974f-2f93f217fea2" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019c1ff6-d7d5-7e80-85ce-01cbf853e7e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_019c1ff6-d7d5-79e6-9ba9-73f34b98b585" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019c1ff6-d7d5-7a53-974f-2f93f217fea2" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_019c1ff6-d7d5-79e6-9ba9-73f34b98b585" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryNet_019c1ff6-d7d5-7381-82aa-19115fc722d8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InventoryNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019c1ff6-d7d5-7a53-974f-2f93f217fea2" xlink:to="loc_us-gaap_InventoryNet_019c1ff6-d7d5-7381-82aa-19115fc722d8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseCurrent_019c1ff6-d7d5-7351-a6f5-f119fe12109d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PrepaidExpenseCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019c1ff6-d7d5-7a53-974f-2f93f217fea2" xlink:to="loc_us-gaap_PrepaidExpenseCurrent_019c1ff6-d7d5-7351-a6f5-f119fe12109d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperationCurrent_019c1ff6-d7d5-768d-8cc0-ed66d7953b68" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperationCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019c1ff6-d7d5-7a53-974f-2f93f217fea2" xlink:to="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperationCurrent_019c1ff6-d7d5-768d-8cc0-ed66d7953b68" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsCurrent_019c1ff6-d7d5-7704-a3ba-5775d4d53dec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019c1ff6-d7d5-7a53-974f-2f93f217fea2" xlink:to="loc_us-gaap_OtherAssetsCurrent_019c1ff6-d7d5-7704-a3ba-5775d4d53dec" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_019c1ff6-d7d5-7882-a8ea-e211b8d31e31" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019c1ff6-d7d5-7a53-974f-2f93f217fea2" xlink:to="loc_us-gaap_AssetsCurrent_019c1ff6-d7d5-7882-a8ea-e211b8d31e31" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsNoncurrentAbstract_019c1ff6-d7d5-70ec-847f-98c020c52d25" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsNoncurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019c1ff6-d7d5-7f64-b820-2b59c3b80b11" xlink:to="loc_us-gaap_AssetsNoncurrentAbstract_019c1ff6-d7d5-70ec-847f-98c020c52d25" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures_019c1ff6-d7d5-7288-96cd-f3ca958697e9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_019c1ff6-d7d5-70ec-847f-98c020c52d25" xlink:to="loc_us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures_019c1ff6-d7d5-7288-96cd-f3ca958697e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_019c1ff6-d7d5-7c99-b1ce-d70f0d9c25eb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_019c1ff6-d7d5-70ec-847f-98c020c52d25" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_019c1ff6-d7d5-7c99-b1ce-d70f0d9c25eb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019c1ff6-d7d5-70ed-af39-184b8ab54b99" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_019c1ff6-d7d5-70ec-847f-98c020c52d25" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019c1ff6-d7d5-70ed-af39-184b8ab54b99" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019c1ff6-d7d5-7f95-acf3-4d64a7dd5d69" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_019c1ff6-d7d5-70ec-847f-98c020c52d25" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019c1ff6-d7d5-7f95-acf3-4d64a7dd5d69" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019c1ff6-d7d5-7944-a29e-cc9b540f24d8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_019c1ff6-d7d5-70ec-847f-98c020c52d25" xlink:to="loc_us-gaap_Goodwill_019c1ff6-d7d5-7944-a29e-cc9b540f24d8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_019c1ff6-d7d5-7790-81cd-5171ea125df5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_019c1ff6-d7d5-70ec-847f-98c020c52d25" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_019c1ff6-d7d5-7790-81cd-5171ea125df5" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_019c1ff6-d7d5-76d7-a110-98c7b258a99c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_019c1ff6-d7d5-70ec-847f-98c020c52d25" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_019c1ff6-d7d5-76d7-a110-98c7b258a99c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetInvestmentInLeaseExcludingAccruedInterestAfterAllowanceForCreditLossNoncurrent_019c1ff6-d7d5-7a07-a880-7f5069d582f2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetInvestmentInLeaseExcludingAccruedInterestAfterAllowanceForCreditLossNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_019c1ff6-d7d5-70ec-847f-98c020c52d25" xlink:to="loc_us-gaap_NetInvestmentInLeaseExcludingAccruedInterestAfterAllowanceForCreditLossNoncurrent_019c1ff6-d7d5-7a07-a880-7f5069d582f2" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesReceivableNet_019c1ff6-d7d5-7098-ade4-774c5510387d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NotesReceivableNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_019c1ff6-d7d5-70ec-847f-98c020c52d25" xlink:to="loc_us-gaap_NotesReceivableNet_019c1ff6-d7d5-7098-ade4-774c5510387d" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_019c1ff6-d7d5-797b-81f8-87ef8c250d2a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_019c1ff6-d7d5-70ec-847f-98c020c52d25" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_019c1ff6-d7d5-797b-81f8-87ef8c250d2a" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsNoncurrent_019c1ff6-d7d5-779d-9da7-ef930c47a305" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_019c1ff6-d7d5-70ec-847f-98c020c52d25" xlink:to="loc_us-gaap_AssetsNoncurrent_019c1ff6-d7d5-779d-9da7-ef930c47a305" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_019c1ff6-d7d5-70f4-b6f2-87e738ebf6d3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019c1ff6-d7d5-7f64-b820-2b59c3b80b11" xlink:to="loc_us-gaap_Assets_019c1ff6-d7d5-70f4-b6f2-87e738ebf6d3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019c1ff6-d7d5-7a92-86e8-ef69a235efeb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019c1ff6-d7d5-74da-980f-a7e78391cc84" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019c1ff6-d7d5-7a92-86e8-ef69a235efeb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_019c1ff6-d7d5-7bc3-9a2c-ea2853504304" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019c1ff6-d7d5-7a92-86e8-ef69a235efeb" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_019c1ff6-d7d5-7bc3-9a2c-ea2853504304" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent_019c1ff6-d7d5-7b3f-bc53-129964fff912" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019c1ff6-d7d5-7bc3-9a2c-ea2853504304" xlink:to="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent_019c1ff6-d7d5-7b3f-bc53-129964fff912" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedIncomeTaxesCurrent_019c1ff6-d7d5-79d0-a58c-c1d1d62b764b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccruedIncomeTaxesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019c1ff6-d7d5-7bc3-9a2c-ea2853504304" xlink:to="loc_us-gaap_AccruedIncomeTaxesCurrent_019c1ff6-d7d5-79d0-a58c-c1d1d62b764b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermBorrowings_019c1ff6-d7d5-7611-89c1-4244d5d4f453" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShortTermBorrowings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019c1ff6-d7d5-7bc3-9a2c-ea2853504304" xlink:to="loc_us-gaap_ShortTermBorrowings_019c1ff6-d7d5-7611-89c1-4244d5d4f453" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtAndCapitalLeaseObligationsCurrent_019c1ff6-d7d5-749d-a4a0-37482a1ac297" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtAndCapitalLeaseObligationsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019c1ff6-d7d5-7bc3-9a2c-ea2853504304" xlink:to="loc_us-gaap_LongTermDebtAndCapitalLeaseObligationsCurrent_019c1ff6-d7d5-749d-a4a0-37482a1ac297" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationCurrent_019c1ff6-d7d5-7271-bacb-568db9c2d181" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019c1ff6-d7d5-7bc3-9a2c-ea2853504304" xlink:to="loc_us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationCurrent_019c1ff6-d7d5-7271-bacb-568db9c2d181" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_019c1ff6-d7d5-77cb-a51c-6e9d8fe3ef65" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019c1ff6-d7d5-7bc3-9a2c-ea2853504304" xlink:to="loc_us-gaap_LiabilitiesCurrent_019c1ff6-d7d5-77cb-a51c-6e9d8fe3ef65" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesNoncurrentAbstract_019c1ff6-d7d5-729b-83a4-5dd60b980ea7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesNoncurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019c1ff6-d7d5-7a92-86e8-ef69a235efeb" xlink:to="loc_us-gaap_LiabilitiesNoncurrentAbstract_019c1ff6-d7d5-729b-83a4-5dd60b980ea7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtAndCapitalLeaseObligations_019c1ff6-d7d5-7993-9173-5c24943b8207" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtAndCapitalLeaseObligations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_019c1ff6-d7d5-729b-83a4-5dd60b980ea7" xlink:to="loc_us-gaap_LongTermDebtAndCapitalLeaseObligations_019c1ff6-d7d5-7993-9173-5c24943b8207" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_019c1ff6-d7d5-7768-87d8-1c988bacd921" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_019c1ff6-d7d5-729b-83a4-5dd60b980ea7" xlink:to="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_019c1ff6-d7d5-7768-87d8-1c988bacd921" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_019c1ff6-d7d5-7b43-834a-56d40ff31e31" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_019c1ff6-d7d5-729b-83a4-5dd60b980ea7" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_019c1ff6-d7d5-7b43-834a-56d40ff31e31" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_019c1ff6-d7d5-782c-8eb6-f16b532ca382" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredIncomeTaxLiabilitiesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_019c1ff6-d7d5-729b-83a4-5dd60b980ea7" xlink:to="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_019c1ff6-d7d5-782c-8eb6-f16b532ca382" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesNoncurrent_019c1ff6-d7d5-7f80-abf8-c1910094343b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract_019c1ff6-d7d5-729b-83a4-5dd60b980ea7" xlink:to="loc_us-gaap_LiabilitiesNoncurrent_019c1ff6-d7d5-7f80-abf8-c1910094343b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_019c1ff6-d7d5-73b1-b387-b5f2eb512756" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019c1ff6-d7d5-7a92-86e8-ef69a235efeb" xlink:to="loc_us-gaap_Liabilities_019c1ff6-d7d5-73b1-b387-b5f2eb512756" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_019c1ff6-d7d5-7a9c-a49a-9e05ba620349" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommitmentsAndContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019c1ff6-d7d5-7a92-86e8-ef69a235efeb" xlink:to="loc_us-gaap_CommitmentsAndContingencies_019c1ff6-d7d5-7a9c-a49a-9e05ba620349" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityAbstract_019c1ff6-d7d5-7cba-8789-18fd85e551c8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019c1ff6-d7d5-7a92-86e8-ef69a235efeb" xlink:to="loc_us-gaap_StockholdersEquityAbstract_019c1ff6-d7d5-7cba-8789-18fd85e551c8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_019c1ff6-d7d5-74b2-a394-01ec48df0971" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019c1ff6-d7d5-7cba-8789-18fd85e551c8" xlink:to="loc_us-gaap_CommonStockValue_019c1ff6-d7d5-74b2-a394-01ec48df0971" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalCommonStock_019c1ff6-d7d5-76ea-b1c1-46bd8836cff2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdditionalPaidInCapitalCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019c1ff6-d7d5-7cba-8789-18fd85e551c8" xlink:to="loc_us-gaap_AdditionalPaidInCapitalCommonStock_019c1ff6-d7d5-76ea-b1c1-46bd8836cff2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019c1ff6-d7d5-7d63-bc6a-71cdfeb787f0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019c1ff6-d7d5-7cba-8789-18fd85e551c8" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019c1ff6-d7d5-7d63-bc6a-71cdfeb787f0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019c1ff6-d7d5-7e0c-976b-ab417e8b0350" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019c1ff6-d7d5-7cba-8789-18fd85e551c8" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019c1ff6-d7d5-7e0c-976b-ab417e8b0350" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonValue_019c1ff6-d7d5-7b9b-840c-137607b8ab17" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockCommonValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019c1ff6-d7d5-7cba-8789-18fd85e551c8" xlink:to="loc_us-gaap_TreasuryStockCommonValue_019c1ff6-d7d5-7b9b-840c-137607b8ab17" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019c1ff6-d7d5-7894-a16f-8cb1cc3bc676" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019c1ff6-d7d5-7cba-8789-18fd85e551c8" xlink:to="loc_us-gaap_StockholdersEquity_019c1ff6-d7d5-7894-a16f-8cb1cc3bc676" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterest_019c1ff6-d7d5-75c7-b635-a6f301320676" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MinorityInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019c1ff6-d7d5-7cba-8789-18fd85e551c8" xlink:to="loc_us-gaap_MinorityInterest_019c1ff6-d7d5-75c7-b635-a6f301320676" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019c1ff6-d7d5-7241-b396-c312cd733f41" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019c1ff6-d7d5-7cba-8789-18fd85e551c8" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019c1ff6-d7d5-7241-b396-c312cd733f41" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_019c1ff6-d7d5-7d49-80b4-15cb0f3f0d9b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019c1ff6-d7d5-7a92-86e8-ef69a235efeb" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_019c1ff6-d7d5-7d49-80b4-15cb0f3f0d9b" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/ConsolidatedBalanceSheetsUnauditedParenthetical" xlink:type="simple" xlink:href="apd-20260331.xsd#ConsolidatedBalanceSheetsUnauditedParenthetical"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/ConsolidatedBalanceSheetsUnauditedParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019c1ff6-d89a-7a50-bf0d-eb5fc7bbc48e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019c1ff6-d89a-7985-a6de-fd90e3006073" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019c1ff6-d89a-7a50-bf0d-eb5fc7bbc48e" xlink:to="loc_us-gaap_StatementTable_019c1ff6-d89a-7985-a6de-fd90e3006073" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019c1ff6-d89a-7310-8f67-6bf548534111" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019c1ff6-d89a-7985-a6de-fd90e3006073" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019c1ff6-d89a-7310-8f67-6bf548534111" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019c1ff6-d89a-7310-8f67-6bf548534111_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019c1ff6-d89a-7310-8f67-6bf548534111" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019c1ff6-d89a-7310-8f67-6bf548534111_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019c1ff6-d89a-7ae4-8925-bfc8b6225179" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019c1ff6-d89a-7310-8f67-6bf548534111" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019c1ff6-d89a-7ae4-8925-bfc8b6225179" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_019c1ff6-d89a-7a75-ac10-fbccc62597e3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableInterestEntityPrimaryBeneficiaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019c1ff6-d89a-7ae4-8925-bfc8b6225179" xlink:to="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_019c1ff6-d89a-7a75-ac10-fbccc62597e3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019c1ff6-d89a-7fb3-ab26-c52465d71e75" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019c1ff6-d89a-7a50-bf0d-eb5fc7bbc48e" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019c1ff6-d89a-7fb3-ab26-c52465d71e75" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_019c1ff6-d89a-7f98-bb4a-c05a52a01a98" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019c1ff6-d89a-7a50-bf0d-eb5fc7bbc48e" xlink:to="loc_us-gaap_CommonStockSharesIssued_019c1ff6-d89a-7f98-bb4a-c05a52a01a98" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_019c1ff6-d89a-7207-8827-ea65ba1e6056" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockCommonShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019c1ff6-d89a-7a50-bf0d-eb5fc7bbc48e" xlink:to="loc_us-gaap_TreasuryStockCommonShares_019c1ff6-d89a-7207-8827-ea65ba1e6056" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_019c1ff6-d89a-7752-93bf-d9e8c5b8205d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019c1ff6-d89a-7a50-bf0d-eb5fc7bbc48e" xlink:to="loc_us-gaap_Assets_019c1ff6-d89a-7752-93bf-d9e8c5b8205d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_019c1ff6-d89a-75ff-bb20-4cde11166d82" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019c1ff6-d89a-7a50-bf0d-eb5fc7bbc48e" xlink:to="loc_us-gaap_Liabilities_019c1ff6-d89a-75ff-bb20-4cde11166d82" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/ConsolidatedStatementsofEquityUnaudited" xlink:type="simple" xlink:href="apd-20260331.xsd#ConsolidatedStatementsofEquityUnaudited"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/ConsolidatedStatementsofEquityUnaudited" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019c1ff6-d89a-798c-bef0-14af7fb8c128" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019c1ff6-d89a-78ce-9c3a-774b953677d9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019c1ff6-d89a-798c-bef0-14af7fb8c128" xlink:to="loc_us-gaap_StatementTable_019c1ff6-d89a-78ce-9c3a-774b953677d9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019c1ff6-d89a-7dce-857e-b4b1c48952e2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019c1ff6-d89a-78ce-9c3a-774b953677d9" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019c1ff6-d89a-7dce-857e-b4b1c48952e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019c1ff6-d89a-7dce-857e-b4b1c48952e2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019c1ff6-d89a-7dce-857e-b4b1c48952e2" xlink:to="loc_us-gaap_EquityComponentDomain_019c1ff6-d89a-7dce-857e-b4b1c48952e2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019c1ff6-d89a-77f2-a22e-7cf20830fe38" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019c1ff6-d89a-7dce-857e-b4b1c48952e2" xlink:to="loc_us-gaap_EquityComponentDomain_019c1ff6-d89a-77f2-a22e-7cf20830fe38" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ParentMember_019c1ff6-d89a-715b-86dc-5ea2ccb42288" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019c1ff6-d89a-77f2-a22e-7cf20830fe38" xlink:to="loc_us-gaap_ParentMember_019c1ff6-d89a-715b-86dc-5ea2ccb42288" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019c1ff6-d89a-759b-9b66-0bc7d9142b64" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_019c1ff6-d89a-715b-86dc-5ea2ccb42288" xlink:to="loc_us-gaap_CommonStockMember_019c1ff6-d89a-759b-9b66-0bc7d9142b64" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019c1ff6-d89a-70e4-9eaa-9806a0685f38" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_019c1ff6-d89a-715b-86dc-5ea2ccb42288" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019c1ff6-d89a-70e4-9eaa-9806a0685f38" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019c1ff6-d89a-7030-a4e7-e1b09424ffde" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_019c1ff6-d89a-715b-86dc-5ea2ccb42288" xlink:to="loc_us-gaap_RetainedEarningsMember_019c1ff6-d89a-7030-a4e7-e1b09424ffde" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019c1ff6-d89a-75a2-8e92-bddfa5509a77" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_019c1ff6-d89a-715b-86dc-5ea2ccb42288" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019c1ff6-d89a-75a2-8e92-bddfa5509a77" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonMember_019c1ff6-d89a-7d7b-8c3c-698602bb1269" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockCommonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_019c1ff6-d89a-715b-86dc-5ea2ccb42288" xlink:to="loc_us-gaap_TreasuryStockCommonMember_019c1ff6-d89a-7d7b-8c3c-698602bb1269" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestMember_019c1ff6-d89a-79dd-ba31-b69f399938a6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019c1ff6-d89a-77f2-a22e-7cf20830fe38" xlink:to="loc_us-gaap_NoncontrollingInterestMember_019c1ff6-d89a-79dd-ba31-b69f399938a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c1ff6-d89a-7d06-a6f7-6c77f0603ae1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019c1ff6-d89a-798c-bef0-14af7fb8c128" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c1ff6-d89a-7d06-a6f7-6c77f0603ae1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019c1ff6-d89a-7c24-996d-851fc2c333c7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c1ff6-d89a-7d06-a6f7-6c77f0603ae1" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019c1ff6-d89a-7c24-996d-851fc2c333c7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossIncludingPortionAttributableToNonredeemableNoncontrollingInterest_019c1ff6-d89a-7f77-a367-723af2e8c05b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLossIncludingPortionAttributableToNonredeemableNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c1ff6-d89a-7d06-a6f7-6c77f0603ae1" xlink:to="loc_us-gaap_NetIncomeLossIncludingPortionAttributableToNonredeemableNoncontrollingInterest_019c1ff6-d89a-7f77-a367-723af2e8c05b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019c1ff6-d89a-7c87-8326-fee445dfe531" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c1ff6-d89a-7d06-a6f7-6c77f0603ae1" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019c1ff6-d89a-7c87-8326-fee445dfe531" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCommonStockCash_019c1ff6-d89a-752b-a67c-7221aba67dc4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DividendsCommonStockCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c1ff6-d89a-7d06-a6f7-6c77f0603ae1" xlink:to="loc_us-gaap_DividendsCommonStockCash_019c1ff6-d89a-752b-a67c-7221aba67dc4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders_019c1ff6-d89a-79df-be08-5c7e8d6b3e61" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c1ff6-d89a-7d06-a6f7-6c77f0603ae1" xlink:to="loc_us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders_019c1ff6-d89a-79df-be08-5c7e8d6b3e61" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019c1ff6-d89a-7e6b-9f7b-533ce7d3d8cd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c1ff6-d89a-7d06-a6f7-6c77f0603ae1" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019c1ff6-d89a-7e6b-9f7b-533ce7d3d8cd" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_019c1ff6-d89a-741c-aa40-68b6351563aa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c1ff6-d89a-7d06-a6f7-6c77f0603ae1" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_019c1ff6-d89a-741c-aa40-68b6351563aa" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestIncreaseFromSaleOfParentEquityInterest_019c1ff6-d89a-7145-9439-03e0b1b7d5f6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NoncontrollingInterestIncreaseFromSaleOfParentEquityInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c1ff6-d89a-7d06-a6f7-6c77f0603ae1" xlink:to="loc_us-gaap_NoncontrollingInterestIncreaseFromSaleOfParentEquityInterest_019c1ff6-d89a-7145-9439-03e0b1b7d5f6" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_NoncontrollingInterestDecreaseIncreaseFromRedemptionsOrPurchaseOfInterests_019c1ff6-d89a-77bf-b32d-57e217db1f9d" xlink:href="apd-20260331.xsd#apd_NoncontrollingInterestDecreaseIncreaseFromRedemptionsOrPurchaseOfInterests"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c1ff6-d89a-7d06-a6f7-6c77f0603ae1" xlink:to="loc_apd_NoncontrollingInterestDecreaseIncreaseFromRedemptionsOrPurchaseOfInterests_019c1ff6-d89a-77bf-b32d-57e217db1f9d" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestDecreaseFromRedemptions_019c1ff6-d89a-72f7-9141-5bca0d67199e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MinorityInterestDecreaseFromRedemptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c1ff6-d89a-7d06-a6f7-6c77f0603ae1" xlink:to="loc_us-gaap_MinorityInterestDecreaseFromRedemptions_019c1ff6-d89a-72f7-9141-5bca0d67199e" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityOther_019c1ff6-d89a-7d1e-88c0-2882b0d597cb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019c1ff6-d89a-7d06-a6f7-6c77f0603ae1" xlink:to="loc_us-gaap_StockholdersEquityOther_019c1ff6-d89a-7d1e-88c0-2882b0d597cb" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019c1ff6-d89a-733c-8e0a-76129aa06fd6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/VariableInterestEntitiesNGHCJointVentureProjectFinancingDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#VariableInterestEntitiesNGHCJointVentureProjectFinancingDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/VariableInterestEntitiesNGHCJointVentureProjectFinancingDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityLineItems_019c1ff6-d89b-7422-90e3-677cd0a5d394" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableInterestEntityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_019c1ff6-d89b-7f36-84d5-74c62dba5623" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfVariableInterestEntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019c1ff6-d89b-7422-90e3-677cd0a5d394" xlink:to="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_019c1ff6-d89b-7f36-84d5-74c62dba5623" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019c1ff6-d89b-775a-8741-29489bafe1f7" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_019c1ff6-d89b-7f36-84d5-74c62dba5623" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019c1ff6-d89b-775a-8741-29489bafe1f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019c1ff6-d89b-775a-8741-29489bafe1f7_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019c1ff6-d89b-775a-8741-29489bafe1f7" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019c1ff6-d89b-775a-8741-29489bafe1f7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019c1ff6-d89b-77ea-aa2a-f0cd120ebeee" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019c1ff6-d89b-775a-8741-29489bafe1f7" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019c1ff6-d89b-77ea-aa2a-f0cd120ebeee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_019c1ff6-d89b-7439-8ad3-e414b5494738" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableInterestEntityPrimaryBeneficiaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019c1ff6-d89b-77ea-aa2a-f0cd120ebeee" xlink:to="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_019c1ff6-d89b-7439-8ad3-e414b5494738" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019c1ff6-d89b-7d2b-a3ab-c3e0b16c4e44" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_019c1ff6-d89b-7f36-84d5-74c62dba5623" xlink:to="loc_us-gaap_DebtInstrumentAxis_019c1ff6-d89b-7d2b-a3ab-c3e0b16c4e44" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019c1ff6-d89b-7d2b-a3ab-c3e0b16c4e44_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019c1ff6-d89b-7d2b-a3ab-c3e0b16c4e44" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019c1ff6-d89b-7d2b-a3ab-c3e0b16c4e44_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019c1ff6-d89b-7122-8d2f-673a2cb755ac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019c1ff6-d89b-7d2b-a3ab-c3e0b16c4e44" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019c1ff6-d89b-7122-8d2f-673a2cb755ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_NEOMGreenHydrogenProjectFinancingPrimaryMember_019c1ff6-d89b-7e05-b984-5e09dee24420" xlink:href="apd-20260331.xsd#apd_NEOMGreenHydrogenProjectFinancingPrimaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019c1ff6-d89b-7122-8d2f-673a2cb755ac" xlink:to="loc_apd_NEOMGreenHydrogenProjectFinancingPrimaryMember_019c1ff6-d89b-7e05-b984-5e09dee24420" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_NEOMGreenHydrogenProjectFinancingWorkingCapitalMember_019c1ff6-d89b-7194-9578-eacd208a9aad" xlink:href="apd-20260331.xsd#apd_NEOMGreenHydrogenProjectFinancingWorkingCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019c1ff6-d89b-7122-8d2f-673a2cb755ac" xlink:to="loc_apd_NEOMGreenHydrogenProjectFinancingWorkingCapitalMember_019c1ff6-d89b-7194-9578-eacd208a9aad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_SaudiRiyalFacilityTwoPointZeroZeroPercentMember_019c1ff6-d89b-7d38-888d-d7768d294c0e" xlink:href="apd-20260331.xsd#apd_SaudiRiyalFacilityTwoPointZeroZeroPercentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019c1ff6-d89b-7122-8d2f-673a2cb755ac" xlink:to="loc_apd_SaudiRiyalFacilityTwoPointZeroZeroPercentMember_019c1ff6-d89b-7d38-888d-d7768d294c0e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_SaudiRiyalLoanFacilityVariableRate5.02Member_019c1ff6-d89b-77df-81c6-f3a0fc7cd799" xlink:href="apd-20260331.xsd#apd_SaudiRiyalLoanFacilityVariableRate5.02Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019c1ff6-d89b-7122-8d2f-673a2cb755ac" xlink:to="loc_apd_SaudiRiyalLoanFacilityVariableRate5.02Member_019c1ff6-d89b-77df-81c6-f3a0fc7cd799" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_DeDesignatedInterestRateSwapsMember_019dbb7c-3ea1-7aa0-a1b6-c75dae72a04d" xlink:href="apd-20260331.xsd#apd_DeDesignatedInterestRateSwapsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019c1ff6-d89b-7122-8d2f-673a2cb755ac" xlink:to="loc_apd_DeDesignatedInterestRateSwapsMember_019dbb7c-3ea1-7aa0-a1b6-c75dae72a04d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RecourseStatusAxis_019c1ff6-d89b-755f-9eb4-ec08e1bbc2be" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RecourseStatusAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_019c1ff6-d89b-7f36-84d5-74c62dba5623" xlink:to="loc_us-gaap_RecourseStatusAxis_019c1ff6-d89b-755f-9eb4-ec08e1bbc2be" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RecourseStatusDomain_019c1ff6-d89b-755f-9eb4-ec08e1bbc2be_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RecourseStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RecourseStatusAxis_019c1ff6-d89b-755f-9eb4-ec08e1bbc2be" xlink:to="loc_us-gaap_RecourseStatusDomain_019c1ff6-d89b-755f-9eb4-ec08e1bbc2be_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RecourseStatusDomain_019c1ff6-d89b-7bfb-a197-11372311250e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RecourseStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RecourseStatusAxis_019c1ff6-d89b-755f-9eb4-ec08e1bbc2be" xlink:to="loc_us-gaap_RecourseStatusDomain_019c1ff6-d89b-7bfb-a197-11372311250e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonrecourseMember_019c1ff6-d89b-71ff-874b-23218f709488" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NonrecourseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RecourseStatusDomain_019c1ff6-d89b-7bfb-a197-11372311250e" xlink:to="loc_us-gaap_NonrecourseMember_019c1ff6-d89b-71ff-874b-23218f709488" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7780-a104-78846f6243ba" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_019c1ff6-d89b-7f36-84d5-74c62dba5623" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7780-a104-78846f6243ba" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7780-a104-78846f6243ba_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7780-a104-78846f6243ba" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7780-a104-78846f6243ba_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7ab2-aea1-92af561a5e52" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7780-a104-78846f6243ba" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7ab2-aea1-92af561a5e52" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_DeDesignatedInterestRateSwapsMember_019c1ff6-d89b-789b-bb1d-095b839384f0" xlink:href="apd-20260331.xsd#apd_DeDesignatedInterestRateSwapsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7ab2-aea1-92af561a5e52" xlink:to="loc_apd_DeDesignatedInterestRateSwapsMember_019c1ff6-d89b-789b-bb1d-095b839384f0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityOwnershipPercentage_019c1ff6-d89b-76f0-aa59-eaaf925045b2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableInterestEntityOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019c1ff6-d89b-7422-90e3-677cd0a5d394" xlink:to="loc_us-gaap_VariableInterestEntityOwnershipPercentage_019c1ff6-d89b-76f0-aa59-eaaf925045b2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_ValueOfEngineeringProcurementAndConstructionAgreement_019c1ff6-d89b-7e1b-b2ba-e66ec517c404" xlink:href="apd-20260331.xsd#apd_ValueOfEngineeringProcurementAndConstructionAgreement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019c1ff6-d89b-7422-90e3-677cd0a5d394" xlink:to="loc_apd_ValueOfEngineeringProcurementAndConstructionAgreement_019c1ff6-d89b-7e1b-b2ba-e66ec517c404" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_ProjectFinancingMaximumBorrowingCapacity_019c1ff6-d89b-7417-818b-7a37dd3b9813" xlink:href="apd-20260331.xsd#apd_ProjectFinancingMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019c1ff6-d89b-7422-90e3-677cd0a5d394" xlink:to="loc_apd_ProjectFinancingMaximumBorrowingCapacity_019c1ff6-d89b-7417-818b-7a37dd3b9813" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_AmountOfExpectedDebtFundingPercent_019c1ff6-d89b-7cb3-a534-fc38be9b6162" xlink:href="apd-20260331.xsd#apd_AmountOfExpectedDebtFundingPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019c1ff6-d89b-7422-90e3-677cd0a5d394" xlink:to="loc_apd_AmountOfExpectedDebtFundingPercent_019c1ff6-d89b-7cb3-a534-fc38be9b6162" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtLongtermAndShorttermCombinedAmount_019c1ff6-d89b-715c-83ab-e49cc652423d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtLongtermAndShorttermCombinedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019c1ff6-d89b-7422-90e3-677cd0a5d394" xlink:to="loc_us-gaap_DebtLongtermAndShorttermCombinedAmount_019c1ff6-d89b-715c-83ab-e49cc652423d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_019c1ff6-d89b-7bfc-95cd-9ac090a0a52c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromIssuanceOfLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019c1ff6-d89b-7422-90e3-677cd0a5d394" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_019c1ff6-d89b-7bfc-95cd-9ac090a0a52c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019c1ff6-d89b-7e49-bbf9-f009f522e75b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019c1ff6-d89b-7422-90e3-677cd0a5d394" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019c1ff6-d89b-7e49-bbf9-f009f522e75b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermBorrowings_019c1ff6-d89b-70a7-b191-0fee0764dee9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShortTermBorrowings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019c1ff6-d89b-7422-90e3-677cd0a5d394" xlink:to="loc_us-gaap_ShortTermBorrowings_019c1ff6-d89b-70a7-b191-0fee0764dee9" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtPercentageBearingVariableInterestRate_019c1ff6-d89b-7d3d-a034-bbeca09a3e10" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtPercentageBearingVariableInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019c1ff6-d89b-7422-90e3-677cd0a5d394" xlink:to="loc_us-gaap_LongTermDebtPercentageBearingVariableInterestRate_019c1ff6-d89b-7d3d-a034-bbeca09a3e10" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_UnrealizedGainLossOnDeDesignatedCashFlowHedgingInstrumentsBeforeTax_019c1ff6-d89b-7020-b055-df40e5ba1f94" xlink:href="apd-20260331.xsd#apd_UnrealizedGainLossOnDeDesignatedCashFlowHedgingInstrumentsBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019c1ff6-d89b-7422-90e3-677cd0a5d394" xlink:to="loc_apd_UnrealizedGainLossOnDeDesignatedCashFlowHedgingInstrumentsBeforeTax_019c1ff6-d89b-7020-b055-df40e5ba1f94" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_UnrealizedGainLossOnDeDesignatedCashFlowHedgingInstrumentsAttributableToNoncontrollingInterests_019c1ff6-d89b-799c-b54c-975b98bf5c04" xlink:href="apd-20260331.xsd#apd_UnrealizedGainLossOnDeDesignatedCashFlowHedgingInstrumentsAttributableToNoncontrollingInterests"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019c1ff6-d89b-7422-90e3-677cd0a5d394" xlink:to="loc_apd_UnrealizedGainLossOnDeDesignatedCashFlowHedgingInstrumentsAttributableToNoncontrollingInterests_019c1ff6-d89b-799c-b54c-975b98bf5c04" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_UnrealizedGainLossOnDeDesignatedCashFlowHedgingInstrumentsAttributableToParentAfterTax_019c1ff6-d89b-7f5d-b044-7968db0fbc3d" xlink:href="apd-20260331.xsd#apd_UnrealizedGainLossOnDeDesignatedCashFlowHedgingInstrumentsAttributableToParentAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019c1ff6-d89b-7422-90e3-677cd0a5d394" xlink:to="loc_apd_UnrealizedGainLossOnDeDesignatedCashFlowHedgingInstrumentsAttributableToParentAfterTax_019c1ff6-d89b-7f5d-b044-7968db0fbc3d" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/VariableInterestEntitiesNGHCJointVentureByBalanceSheetItemsDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#VariableInterestEntitiesNGHCJointVentureByBalanceSheetItemsDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/VariableInterestEntitiesNGHCJointVentureByBalanceSheetItemsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityLineItems_019c1ff6-d89b-7e31-9208-ce37d4320d96" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableInterestEntityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_019c1ff6-d89b-715b-b1da-68271363b674" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfVariableInterestEntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019c1ff6-d89b-7e31-9208-ce37d4320d96" xlink:to="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_019c1ff6-d89b-715b-b1da-68271363b674" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019c1ff6-d89b-71eb-8e44-06c977bca540" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_019c1ff6-d89b-715b-b1da-68271363b674" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019c1ff6-d89b-71eb-8e44-06c977bca540" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019c1ff6-d89b-71eb-8e44-06c977bca540_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019c1ff6-d89b-71eb-8e44-06c977bca540" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019c1ff6-d89b-71eb-8e44-06c977bca540_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019c1ff6-d89b-73f9-a5c7-0d0709d37b16" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019c1ff6-d89b-71eb-8e44-06c977bca540" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019c1ff6-d89b-73f9-a5c7-0d0709d37b16" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_019c1ff6-d89b-78dd-aae5-006d4eea2a66" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableInterestEntityPrimaryBeneficiaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019c1ff6-d89b-73f9-a5c7-0d0709d37b16" xlink:to="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_019c1ff6-d89b-78dd-aae5-006d4eea2a66" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_019c1ff6-d89b-7fe2-8525-cf1fedeecca7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019c1ff6-d89b-7e31-9208-ce37d4320d96" xlink:to="loc_us-gaap_AssetsAbstract_019c1ff6-d89b-7fe2-8525-cf1fedeecca7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019c1ff6-d89b-7e59-bf70-35dfff93ff39" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019c1ff6-d89b-7fe2-8525-cf1fedeecca7" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019c1ff6-d89b-7e59-bf70-35dfff93ff39" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_019c1ff6-d89b-7633-9aa5-def605303c25" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019c1ff6-d89b-7fe2-8525-cf1fedeecca7" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_019c1ff6-d89b-7633-9aa5-def605303c25" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseCurrent_019c1ff6-d89b-7ffc-ad49-aee6a19cb648" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PrepaidExpenseCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019c1ff6-d89b-7fe2-8525-cf1fedeecca7" xlink:to="loc_us-gaap_PrepaidExpenseCurrent_019c1ff6-d89b-7ffc-ad49-aee6a19cb648" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsCurrent_019c1ff6-d89b-7cce-bc54-0a165cbb2b6e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019c1ff6-d89b-7fe2-8525-cf1fedeecca7" xlink:to="loc_us-gaap_OtherAssetsCurrent_019c1ff6-d89b-7cce-bc54-0a165cbb2b6e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_019c1ff6-d89b-7e3d-a89c-26548506cab8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019c1ff6-d89b-7fe2-8525-cf1fedeecca7" xlink:to="loc_us-gaap_AssetsCurrent_019c1ff6-d89b-7e3d-a89c-26548506cab8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019c1ff6-d89b-7d74-8dbb-d8d02c31db6f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019c1ff6-d89b-7fe2-8525-cf1fedeecca7" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019c1ff6-d89b-7d74-8dbb-d8d02c31db6f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_019c1ff6-d89b-7990-af24-56ee972c3142" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019c1ff6-d89b-7fe2-8525-cf1fedeecca7" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_019c1ff6-d89b-7990-af24-56ee972c3142" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_019c1ff6-d89b-7bc9-854c-e6df7e172f6d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019c1ff6-d89b-7fe2-8525-cf1fedeecca7" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_019c1ff6-d89b-7bc9-854c-e6df7e172f6d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsNoncurrent_019c1ff6-d89b-7650-9487-e5b96dd384aa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019c1ff6-d89b-7fe2-8525-cf1fedeecca7" xlink:to="loc_us-gaap_AssetsNoncurrent_019c1ff6-d89b-7650-9487-e5b96dd384aa" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_019c1ff6-d89b-7010-8adc-78885f5f5978" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019c1ff6-d89b-7fe2-8525-cf1fedeecca7" xlink:to="loc_us-gaap_Assets_019c1ff6-d89b-7010-8adc-78885f5f5978" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAbstract_019c1ff6-d89b-75f3-ab02-7dcf70c597f4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019c1ff6-d89b-7e31-9208-ce37d4320d96" xlink:to="loc_us-gaap_LiabilitiesAbstract_019c1ff6-d89b-75f3-ab02-7dcf70c597f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent_019c1ff6-d89b-70d8-97b1-e6e211ca540a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019c1ff6-d89b-75f3-ab02-7dcf70c597f4" xlink:to="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent_019c1ff6-d89b-70d8-97b1-e6e211ca540a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedIncomeTaxesCurrent_019c1ff6-d89b-7150-9c0c-89fb2a50adbc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccruedIncomeTaxesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019c1ff6-d89b-75f3-ab02-7dcf70c597f4" xlink:to="loc_us-gaap_AccruedIncomeTaxesCurrent_019c1ff6-d89b-7150-9c0c-89fb2a50adbc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermBorrowings_019c1ff6-d89b-7da8-90e8-5fc542f81ac3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShortTermBorrowings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019c1ff6-d89b-75f3-ab02-7dcf70c597f4" xlink:to="loc_us-gaap_ShortTermBorrowings_019c1ff6-d89b-7da8-90e8-5fc542f81ac3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_019c1ff6-d89b-7acb-af7b-f05427b51013" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019c1ff6-d89b-75f3-ab02-7dcf70c597f4" xlink:to="loc_us-gaap_LiabilitiesCurrent_019c1ff6-d89b-7acb-af7b-f05427b51013" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtAndCapitalLeaseObligations_019c1ff6-d89b-75f5-b7c9-6ed428243d44" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtAndCapitalLeaseObligations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019c1ff6-d89b-75f3-ab02-7dcf70c597f4" xlink:to="loc_us-gaap_LongTermDebtAndCapitalLeaseObligations_019c1ff6-d89b-75f5-b7c9-6ed428243d44" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_019c1ff6-d89b-7de3-b762-1614bd68ab8a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019c1ff6-d89b-75f3-ab02-7dcf70c597f4" xlink:to="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_019c1ff6-d89b-7de3-b762-1614bd68ab8a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_019c1ff6-d89b-760e-800b-3829147b5fa9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019c1ff6-d89b-75f3-ab02-7dcf70c597f4" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_019c1ff6-d89b-760e-800b-3829147b5fa9" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_019c1ff6-d89b-7aec-addd-d73d3606237e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredIncomeTaxLiabilitiesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019c1ff6-d89b-75f3-ab02-7dcf70c597f4" xlink:to="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_019c1ff6-d89b-7aec-addd-d73d3606237e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesNoncurrent_019c1ff6-d89b-7b34-8ed0-4c771a992f4b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019c1ff6-d89b-75f3-ab02-7dcf70c597f4" xlink:to="loc_us-gaap_LiabilitiesNoncurrent_019c1ff6-d89b-7b34-8ed0-4c771a992f4b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_019c1ff6-d89b-7921-b2ec-f294d1ecf654" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_019c1ff6-d89b-75f3-ab02-7dcf70c597f4" xlink:to="loc_us-gaap_Liabilities_019c1ff6-d89b-7921-b2ec-f294d1ecf654" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityAbstract_019c1ff6-d89b-7d3c-8532-4eb2cea3ab03" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019c1ff6-d89b-7e31-9208-ce37d4320d96" xlink:to="loc_us-gaap_EquityAbstract_019c1ff6-d89b-7d3c-8532-4eb2cea3ab03" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019c1ff6-d89b-7599-becc-13fc6f9c3bef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityAbstract_019c1ff6-d89b-7d3c-8532-4eb2cea3ab03" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019c1ff6-d89b-7599-becc-13fc6f9c3bef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterest_019c1ff6-d89b-7b39-abbc-e12150884194" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MinorityInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityAbstract_019c1ff6-d89b-7d3c-8532-4eb2cea3ab03" xlink:to="loc_us-gaap_MinorityInterest_019c1ff6-d89b-7b39-abbc-e12150884194" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/VariableInterestEntitiesJIGPCJointVentureDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#VariableInterestEntitiesJIGPCJointVentureDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/VariableInterestEntitiesJIGPCJointVentureDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019c1ff6-d89b-734f-97e8-e7a41d48fa82" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019c1ff6-d89b-7e5a-b43f-dfb04759e873" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019c1ff6-d89b-734f-97e8-e7a41d48fa82" xlink:to="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019c1ff6-d89b-7e5a-b43f-dfb04759e873" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019c1ff6-d89b-7217-aad5-604b4e2ba6ed" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019c1ff6-d89b-7e5a-b43f-dfb04759e873" xlink:to="loc_dei_LegalEntityAxis_019c1ff6-d89b-7217-aad5-604b4e2ba6ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019c1ff6-d89b-7217-aad5-604b4e2ba6ed_default" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019c1ff6-d89b-7217-aad5-604b4e2ba6ed" xlink:to="loc_dei_EntityDomain_019c1ff6-d89b-7217-aad5-604b4e2ba6ed_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019c1ff6-d89b-767f-8b8b-2ab5c20e4d53" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019c1ff6-d89b-7217-aad5-604b4e2ba6ed" xlink:to="loc_dei_EntityDomain_019c1ff6-d89b-767f-8b8b-2ab5c20e4d53" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_JazanIntegratedGasificationAndPowerCompanyMember_019c1ff6-d89b-7e7f-8ebd-786ab79bedd5" xlink:href="apd-20260331.xsd#apd_JazanIntegratedGasificationAndPowerCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019c1ff6-d89b-767f-8b8b-2ab5c20e4d53" xlink:to="loc_apd_JazanIntegratedGasificationAndPowerCompanyMember_019c1ff6-d89b-7e7f-8ebd-786ab79bedd5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019c1ff6-d89b-7d45-9dff-901ff7d1a588" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019c1ff6-d89b-7e5a-b43f-dfb04759e873" xlink:to="loc_srt_CounterpartyNameAxis_019c1ff6-d89b-7d45-9dff-901ff7d1a588" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019c1ff6-d89b-7d45-9dff-901ff7d1a588_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019c1ff6-d89b-7d45-9dff-901ff7d1a588" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019c1ff6-d89b-7d45-9dff-901ff7d1a588_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019c1ff6-d89b-7b51-9a4d-a9087a3c3ec8" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019c1ff6-d89b-7d45-9dff-901ff7d1a588" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019c1ff6-d89b-7b51-9a4d-a9087a3c3ec8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_AramcoMember_019c1ff6-d89b-7e1c-aa19-d051c6c0484d" xlink:href="apd-20260331.xsd#apd_AramcoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019c1ff6-d89b-7b51-9a4d-a9087a3c3ec8" xlink:to="loc_apd_AramcoMember_019c1ff6-d89b-7e1c-aa19-d051c6c0484d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019c1ff6-d89b-78dd-9fca-66d66d96e974" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019c1ff6-d89b-7e5a-b43f-dfb04759e873" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019c1ff6-d89b-78dd-9fca-66d66d96e974" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019c1ff6-d89b-78dd-9fca-66d66d96e974_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019c1ff6-d89b-78dd-9fca-66d66d96e974" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019c1ff6-d89b-78dd-9fca-66d66d96e974_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019c1ff6-d89b-7f72-b638-2987f351ae1d" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019c1ff6-d89b-78dd-9fca-66d66d96e974" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019c1ff6-d89b-7f72-b638-2987f351ae1d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_JazanIntegratedGasificationAndPowerCompanyMember_019c1ff6-d89b-723c-bf51-c6ca552cdae5" xlink:href="apd-20260331.xsd#apd_JazanIntegratedGasificationAndPowerCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019c1ff6-d89b-7f72-b638-2987f351ae1d" xlink:to="loc_apd_JazanIntegratedGasificationAndPowerCompanyMember_019c1ff6-d89b-723c-bf51-c6ca552cdae5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_TermOfProjectAgreement_019c1ff6-d89b-7e31-8111-f36f8111b661" xlink:href="apd-20260331.xsd#apd_TermOfProjectAgreement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019c1ff6-d89b-734f-97e8-e7a41d48fa82" xlink:to="loc_apd_TermOfProjectAgreement_019c1ff6-d89b-7e31-8111-f36f8111b661" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_019c1ff6-d89b-7065-aa2d-335459452e4b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestmentOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019c1ff6-d89b-734f-97e8-e7a41d48fa82" xlink:to="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_019c1ff6-d89b-7065-aa2d-335459452e4b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_EquityMethodInvestmentOwnershipPercentageAttributableToNoncontrollingPartner_019c1ff6-d89b-791c-9cf4-d480aaf9bb14" xlink:href="apd-20260331.xsd#apd_EquityMethodInvestmentOwnershipPercentageAttributableToNoncontrollingPartner"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019c1ff6-d89b-734f-97e8-e7a41d48fa82" xlink:to="loc_apd_EquityMethodInvestmentOwnershipPercentageAttributableToNoncontrollingPartner_019c1ff6-d89b-791c-9cf4-d480aaf9bb14" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestments_019c1ff6-d89b-7bbe-98fa-5990c4e5b6aa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019c1ff6-d89b-734f-97e8-e7a41d48fa82" xlink:to="loc_us-gaap_EquityMethodInvestments_019c1ff6-d89b-7bbe-98fa-5990c4e5b6aa" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/VariableInterestEntitiesWorldEnergyDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#VariableInterestEntitiesWorldEnergyDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/VariableInterestEntitiesWorldEnergyDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityLineItems_019c1ff6-d89b-7794-85cb-946ea119f273" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableInterestEntityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_019c1ff6-d89b-7249-9afe-ff2b3ad556cd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfVariableInterestEntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019c1ff6-d89b-7794-85cb-946ea119f273" xlink:to="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_019c1ff6-d89b-7249-9afe-ff2b3ad556cd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionAxis_019c1ff6-d89b-7216-a7c4-f7a788f684b0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_019c1ff6-d89b-7249-9afe-ff2b3ad556cd" xlink:to="loc_us-gaap_AssetAcquisitionAxis_019c1ff6-d89b-7216-a7c4-f7a788f684b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionDomain_019c1ff6-d89b-7216-a7c4-f7a788f684b0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetAcquisitionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AssetAcquisitionAxis_019c1ff6-d89b-7216-a7c4-f7a788f684b0" xlink:to="loc_us-gaap_AssetAcquisitionDomain_019c1ff6-d89b-7216-a7c4-f7a788f684b0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionDomain_019c1ff6-d89b-7b19-a0d7-b1fe5accee86" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetAcquisitionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AssetAcquisitionAxis_019c1ff6-d89b-7216-a7c4-f7a788f684b0" xlink:to="loc_us-gaap_AssetAcquisitionDomain_019c1ff6-d89b-7b19-a0d7-b1fe5accee86" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_WorldEnergyMember_019c1ff6-d89b-7fb6-b842-22155d044aef" xlink:href="apd-20260331.xsd#apd_WorldEnergyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetAcquisitionDomain_019c1ff6-d89b-7b19-a0d7-b1fe5accee86" xlink:to="loc_apd_WorldEnergyMember_019c1ff6-d89b-7fb6-b842-22155d044aef" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_019c1ff6-d89b-7903-b676-b14440dd37e5" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_019c1ff6-d89b-7249-9afe-ff2b3ad556cd" xlink:to="loc_srt_ConsolidatedEntitiesAxis_019c1ff6-d89b-7903-b676-b14440dd37e5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019c1ff6-d89b-7903-b676-b14440dd37e5_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019c1ff6-d89b-7903-b676-b14440dd37e5" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019c1ff6-d89b-7903-b676-b14440dd37e5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_019c1ff6-d89b-70cb-b0eb-15aa51fcc5e7" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_019c1ff6-d89b-7903-b676-b14440dd37e5" xlink:to="loc_srt_ConsolidatedEntitiesDomain_019c1ff6-d89b-70cb-b0eb-15aa51fcc5e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember_019c1ff6-d89b-7869-9184-bdb2bee7fd1f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_019c1ff6-d89b-70cb-b0eb-15aa51fcc5e7" xlink:to="loc_us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember_019c1ff6-d89b-7869-9184-bdb2bee7fd1f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessExitCosts1_019c1ff6-d89b-7b0b-b292-7707f81e410c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessExitCosts1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_019c1ff6-d89b-7794-85cb-946ea119f273" xlink:to="loc_us-gaap_BusinessExitCosts1_019c1ff6-d89b-7b0b-b292-7707f81e410c" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/BusinessandAssetActionsNarrativeDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#BusinessandAssetActionsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/BusinessandAssetActionsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_019db70c-f7a7-776f-9cf4-53b95bda262d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019db70c-f7a7-7c83-90fc-616ae53fe1e9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019db70c-f7a7-776f-9cf4-53b95bda262d" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019db70c-f7a7-7c83-90fc-616ae53fe1e9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanAxis_019db70c-f7a7-7cc6-8995-a827a20f605d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019db70c-f7a7-7c83-90fc-616ae53fe1e9" xlink:to="loc_us-gaap_RestructuringPlanAxis_019db70c-f7a7-7cc6-8995-a827a20f605d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_019db70c-f7a7-7cc6-8995-a827a20f605d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringPlanAxis_019db70c-f7a7-7cc6-8995-a827a20f605d" xlink:to="loc_us-gaap_RestructuringPlanDomain_019db70c-f7a7-7cc6-8995-a827a20f605d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_019db70c-f7a7-74c1-9d97-c4996251c946" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringPlanAxis_019db70c-f7a7-7cc6-8995-a827a20f605d" xlink:to="loc_us-gaap_RestructuringPlanDomain_019db70c-f7a7-74c1-9d97-c4996251c946" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_ProjectExitCostsMember_019db70c-f7a7-7353-80d0-2797c512dce8" xlink:href="apd-20260331.xsd#apd_ProjectExitCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_019db70c-f7a7-74c1-9d97-c4996251c946" xlink:to="loc_apd_ProjectExitCostsMember_019db70c-f7a7-7353-80d0-2797c512dce8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_019db70c-f7a7-73ab-ba6c-d0a934b87c4f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019db70c-f7a7-7c83-90fc-616ae53fe1e9" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_019db70c-f7a7-73ab-ba6c-d0a934b87c4f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_019db70c-f7a7-73ab-ba6c-d0a934b87c4f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_019db70c-f7a7-73ab-ba6c-d0a934b87c4f" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_019db70c-f7a7-73ab-ba6c-d0a934b87c4f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_019db70c-f7a7-7e35-9854-70cfb775a0f4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_019db70c-f7a7-73ab-ba6c-d0a934b87c4f" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_019db70c-f7a7-7e35-9854-70cfb775a0f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLossMember_019db70c-f7a7-792f-8886-52fbe3cc02af" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingIncomeLossMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_019db70c-f7a7-7e35-9854-70cfb775a0f4" xlink:to="loc_us-gaap_OperatingIncomeLossMember_019db70c-f7a7-792f-8886-52fbe3cc02af" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpenseMember_019db70c-f7a7-7fad-bf0d-485e44664da5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherNonoperatingIncomeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_019db70c-f7a7-7e35-9854-70cfb775a0f4" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpenseMember_019db70c-f7a7-7fad-bf0d-485e44664da5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_IncomeLossFromEquityMethodInvestmentsMember_019db70c-f7a7-7657-9613-e78f7c4011c6" xlink:href="apd-20260331.xsd#apd_IncomeLossFromEquityMethodInvestmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_019db70c-f7a7-7e35-9854-70cfb775a0f4" xlink:to="loc_apd_IncomeLossFromEquityMethodInvestmentsMember_019db70c-f7a7-7657-9613-e78f7c4011c6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessExitCosts1_019db70c-f7a7-73f4-8f0b-3f01cc3c2c2c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessExitCosts1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019db70c-f7a7-776f-9cf4-53b95bda262d" xlink:to="loc_us-gaap_BusinessExitCosts1_019db70c-f7a7-73f4-8f0b-3f01cc3c2c2c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringSettlementAndImpairmentProvisions_019db70c-f7a7-7515-af89-14bc123f956b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringSettlementAndImpairmentProvisions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019db70c-f7a7-776f-9cf4-53b95bda262d" xlink:to="loc_us-gaap_RestructuringSettlementAndImpairmentProvisions_019db70c-f7a7-7515-af89-14bc123f956b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_RestructuringChargesAttributableToParentAfterTax_019db70c-f7a7-7bd8-a4c5-e7fdaa9e78ba" xlink:href="apd-20260331.xsd#apd_RestructuringChargesAttributableToParentAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019db70c-f7a7-776f-9cf4-53b95bda262d" xlink:to="loc_apd_RestructuringChargesAttributableToParentAfterTax_019db70c-f7a7-7bd8-a4c5-e7fdaa9e78ba" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_RestructuringChargesIncludingEquityAffiliateIncome_019db70c-f7a7-73a6-b789-37e3ae46530c" xlink:href="apd-20260331.xsd#apd_RestructuringChargesIncludingEquityAffiliateIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019db70c-f7a7-776f-9cf4-53b95bda262d" xlink:to="loc_apd_RestructuringChargesIncludingEquityAffiliateIncome_019db70c-f7a7-73a6-b789-37e3ae46530c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_RestructuringChargesIncludingEquityAffiliateIncomeAttributableToParentAfterTax_019db70c-f7a7-7e24-afbe-8584efc02f87" xlink:href="apd-20260331.xsd#apd_RestructuringChargesIncludingEquityAffiliateIncomeAttributableToParentAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019db70c-f7a7-776f-9cf4-53b95bda262d" xlink:to="loc_apd_RestructuringChargesIncludingEquityAffiliateIncomeAttributableToParentAfterTax_019db70c-f7a7-7e24-afbe-8584efc02f87" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_RestructuringChargesAttributableToNoncontrollingInterest_019db70c-f7a7-7178-9e79-850a429783b4" xlink:href="apd-20260331.xsd#apd_RestructuringChargesAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019db70c-f7a7-776f-9cf4-53b95bda262d" xlink:to="loc_apd_RestructuringChargesAttributableToNoncontrollingInterest_019db70c-f7a7-7178-9e79-850a429783b4" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/BusinessandAssetActionsProjectExitCostsDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#BusinessandAssetActionsProjectExitCostsDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/BusinessandAssetActionsProjectExitCostsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_019c1ff6-d89b-72d9-b46f-67cfd3fcc426" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019c1ff6-d89b-74fa-84fc-5ed281361850" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019c1ff6-d89b-72d9-b46f-67cfd3fcc426" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019c1ff6-d89b-74fa-84fc-5ed281361850" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanAxis_019c1ff6-d89b-72f1-a4ad-b168b3ca80ce" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019c1ff6-d89b-74fa-84fc-5ed281361850" xlink:to="loc_us-gaap_RestructuringPlanAxis_019c1ff6-d89b-72f1-a4ad-b168b3ca80ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_019c1ff6-d89b-72f1-a4ad-b168b3ca80ce_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringPlanAxis_019c1ff6-d89b-72f1-a4ad-b168b3ca80ce" xlink:to="loc_us-gaap_RestructuringPlanDomain_019c1ff6-d89b-72f1-a4ad-b168b3ca80ce_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_019c1ff6-d89b-7357-aa45-da1bcce4a39b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringPlanAxis_019c1ff6-d89b-72f1-a4ad-b168b3ca80ce" xlink:to="loc_us-gaap_RestructuringPlanDomain_019c1ff6-d89b-7357-aa45-da1bcce4a39b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_ProjectExitCostsMember_019c1ff6-d89b-759a-a0a0-1a4d1b30c00b" xlink:href="apd-20260331.xsd#apd_ProjectExitCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_019c1ff6-d89b-7357-aa45-da1bcce4a39b" xlink:to="loc_apd_ProjectExitCostsMember_019c1ff6-d89b-759a-a0a0-1a4d1b30c00b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessExitCosts1_019db70f-a6f1-7564-92a8-ae0772947990" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessExitCosts1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019c1ff6-d89b-72d9-b46f-67cfd3fcc426" xlink:to="loc_us-gaap_BusinessExitCosts1_019db70f-a6f1-7564-92a8-ae0772947990" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveSettledWithoutCash2_019db70f-a6f1-73cc-a8da-4084df1482aa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringReserveSettledWithoutCash2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019c1ff6-d89b-72d9-b46f-67cfd3fcc426" xlink:to="loc_us-gaap_RestructuringReserveSettledWithoutCash2_019db70f-a6f1-73cc-a8da-4084df1482aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfLongLivedAssetsToBeDisposedOf_019db70f-a6f1-7aae-ac75-32ee337d7210" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ImpairmentOfLongLivedAssetsToBeDisposedOf"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019c1ff6-d89b-72d9-b46f-67cfd3fcc426" xlink:to="loc_us-gaap_ImpairmentOfLongLivedAssetsToBeDisposedOf_019db70f-a6f1-7aae-ac75-32ee337d7210" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_TotalExpectedCashOutFlow_019db70f-a6f1-7637-a253-ddb338efc012" xlink:href="apd-20260331.xsd#apd_TotalExpectedCashOutFlow"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019c1ff6-d89b-72d9-b46f-67cfd3fcc426" xlink:to="loc_apd_TotalExpectedCashOutFlow_019db70f-a6f1-7637-a253-ddb338efc012" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveRollForward_019c1ff6-d89b-73b5-beb0-a279e278c4d9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringReserveRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019c1ff6-d89b-72d9-b46f-67cfd3fcc426" xlink:to="loc_us-gaap_RestructuringReserveRollForward_019c1ff6-d89b-73b5-beb0-a279e278c4d9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveCurrent_019c1ff6-d89b-7d80-88c3-85af3279b721" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringReserveCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_019c1ff6-d89b-73b5-beb0-a279e278c4d9" xlink:to="loc_us-gaap_RestructuringReserveCurrent_019c1ff6-d89b-7d80-88c3-85af3279b721" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveAccrualAdjustment1_019c1ff6-d89b-784f-a341-38266c010d9f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringReserveAccrualAdjustment1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_019c1ff6-d89b-73b5-beb0-a279e278c4d9" xlink:to="loc_us-gaap_RestructuringReserveAccrualAdjustment1_019c1ff6-d89b-784f-a341-38266c010d9f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRestructuring_019c1ff6-d89b-7c2b-bf6b-12219ac02f79" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsForRestructuring"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_019c1ff6-d89b-73b5-beb0-a279e278c4d9" xlink:to="loc_us-gaap_PaymentsForRestructuring_019c1ff6-d89b-7c2b-bf6b-12219ac02f79" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveTranslationAdjustment_019c1ff6-d89b-7b9b-9482-e05408da0c21" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringReserveTranslationAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_019c1ff6-d89b-73b5-beb0-a279e278c4d9" xlink:to="loc_us-gaap_RestructuringReserveTranslationAdjustment_019c1ff6-d89b-7b9b-9482-e05408da0c21" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveCurrent_019c1ff6-d89b-714c-a94d-1c6f5c34aceb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringReserveCurrent"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/BusinessandAssetActionsGlobalCostReductionPlanDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#BusinessandAssetActionsGlobalCostReductionPlanDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/BusinessandAssetActionsGlobalCostReductionPlanDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_019c1ff6-d89b-7313-8255-d586547543e0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019c1ff6-d89b-7cac-9557-acdd8ff7f114" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019c1ff6-d89b-7313-8255-d586547543e0" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019c1ff6-d89b-7cac-9557-acdd8ff7f114" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanAxis_019c1ff6-d89b-7b58-818a-4cd3455b1d1c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019c1ff6-d89b-7cac-9557-acdd8ff7f114" xlink:to="loc_us-gaap_RestructuringPlanAxis_019c1ff6-d89b-7b58-818a-4cd3455b1d1c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_019c1ff6-d89b-7b58-818a-4cd3455b1d1c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringPlanAxis_019c1ff6-d89b-7b58-818a-4cd3455b1d1c" xlink:to="loc_us-gaap_RestructuringPlanDomain_019c1ff6-d89b-7b58-818a-4cd3455b1d1c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_019c1ff6-d89b-75ee-b26a-a30d70194140" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringPlanAxis_019c1ff6-d89b-7b58-818a-4cd3455b1d1c" xlink:to="loc_us-gaap_RestructuringPlanDomain_019c1ff6-d89b-75ee-b26a-a30d70194140" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_GlobalCostReductionPlanMember_019c1ff6-d89b-7638-8223-c041ed95bada" xlink:href="apd-20260331.xsd#apd_GlobalCostReductionPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_019c1ff6-d89b-75ee-b26a-a30d70194140" xlink:to="loc_apd_GlobalCostReductionPlanMember_019c1ff6-d89b-7638-8223-c041ed95bada" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeveranceCosts1_019c1ff6-d89b-7a79-8018-18f5edfb0fe6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SeveranceCosts1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019c1ff6-d89b-7313-8255-d586547543e0" xlink:to="loc_us-gaap_SeveranceCosts1_019c1ff6-d89b-7a79-8018-18f5edfb0fe6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringAndRelatedCostExpectedNumberOfPositionsEliminated_019c1ff6-d89b-7afc-a5fc-4910943fe578" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringAndRelatedCostExpectedNumberOfPositionsEliminated"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019c1ff6-d89b-7313-8255-d586547543e0" xlink:to="loc_us-gaap_RestructuringAndRelatedCostExpectedNumberOfPositionsEliminated_019c1ff6-d89b-7afc-a5fc-4910943fe578" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveRollForward_019c1ff6-d89b-7af8-877e-22aa87422158" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringReserveRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019c1ff6-d89b-7313-8255-d586547543e0" xlink:to="loc_us-gaap_RestructuringReserveRollForward_019c1ff6-d89b-7af8-877e-22aa87422158" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveCurrent_019c1ff6-d89b-7c7d-a976-d4bf9934a642" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringReserveCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_019c1ff6-d89b-7af8-877e-22aa87422158" xlink:to="loc_us-gaap_RestructuringReserveCurrent_019c1ff6-d89b-7c7d-a976-d4bf9934a642" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRestructuring_019c1ff6-d89b-751b-84b0-b1661f6bf269" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsForRestructuring"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_019c1ff6-d89b-7af8-877e-22aa87422158" xlink:to="loc_us-gaap_PaymentsForRestructuring_019c1ff6-d89b-751b-84b0-b1661f6bf269" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveTranslationAdjustment_019c1ff6-d89b-74fb-b003-566238ebf16c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringReserveTranslationAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_019c1ff6-d89b-7af8-877e-22aa87422158" xlink:to="loc_us-gaap_RestructuringReserveTranslationAdjustment_019c1ff6-d89b-74fb-b003-566238ebf16c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveCurrent_019c1ff6-d89b-77e6-a64c-6fa494b980e4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringReserveCurrent"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/RevenueRecognitionDisaggregationofRevenueDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#RevenueRecognitionDisaggregationofRevenueDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/RevenueRecognitionDisaggregationofRevenueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019c1ff6-d89b-792e-9486-63219c57258a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_019c1ff6-d89b-7c16-811c-86bdd9da0db0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019c1ff6-d89b-792e-9486-63219c57258a" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019c1ff6-d89b-7c16-811c-86bdd9da0db0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019c1ff6-d89b-794b-82b1-ea7400bce467" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019c1ff6-d89b-7c16-811c-86bdd9da0db0" xlink:to="loc_srt_ProductOrServiceAxis_019c1ff6-d89b-794b-82b1-ea7400bce467" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019c1ff6-d89b-794b-82b1-ea7400bce467_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019c1ff6-d89b-794b-82b1-ea7400bce467" xlink:to="loc_srt_ProductsAndServicesDomain_019c1ff6-d89b-794b-82b1-ea7400bce467_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019c1ff6-d89b-75d5-a808-8be93c30f451" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019c1ff6-d89b-794b-82b1-ea7400bce467" xlink:to="loc_srt_ProductsAndServicesDomain_019c1ff6-d89b-75d5-a808-8be93c30f451" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_OnsiteMember_019c1ff6-d89b-70b7-b455-0f95592706fb" xlink:href="apd-20260331.xsd#apd_OnsiteMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019c1ff6-d89b-75d5-a808-8be93c30f451" xlink:to="loc_apd_OnsiteMember_019c1ff6-d89b-70b7-b455-0f95592706fb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_MerchantMember_019c1ff6-d89b-7444-90e0-c3c655c087da" xlink:href="apd-20260331.xsd#apd_MerchantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019c1ff6-d89b-75d5-a808-8be93c30f451" xlink:to="loc_apd_MerchantMember_019c1ff6-d89b-7444-90e0-c3c655c087da" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_SaleofEquipmentMember_019c1ff6-d89b-7561-8b06-ec974f82ae71" xlink:href="apd-20260331.xsd#apd_SaleofEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019c1ff6-d89b-75d5-a808-8be93c30f451" xlink:to="loc_apd_SaleofEquipmentMember_019c1ff6-d89b-7561-8b06-ec974f82ae71" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_FinancingAndLeaseArrangmentMember_019c1ff6-d89b-7c08-8e68-ed4d4b8a7992" xlink:href="apd-20260331.xsd#apd_FinancingAndLeaseArrangmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019c1ff6-d89b-75d5-a808-8be93c30f451" xlink:to="loc_apd_FinancingAndLeaseArrangmentMember_019c1ff6-d89b-7c08-8e68-ed4d4b8a7992" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019c1ff6-d89b-7a3e-91f7-ad3cb5d5308c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019c1ff6-d89b-7c16-811c-86bdd9da0db0" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019c1ff6-d89b-7a3e-91f7-ad3cb5d5308c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019c1ff6-d89b-7a3e-91f7-ad3cb5d5308c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019c1ff6-d89b-7a3e-91f7-ad3cb5d5308c" xlink:to="loc_us-gaap_SegmentDomain_019c1ff6-d89b-7a3e-91f7-ad3cb5d5308c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019c1ff6-d89b-70dc-abdd-f6fa3672a228" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019c1ff6-d89b-7a3e-91f7-ad3cb5d5308c" xlink:to="loc_us-gaap_SegmentDomain_019c1ff6-d89b-70dc-abdd-f6fa3672a228" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_AmericasSegmentMember_019c1ff6-d89b-7802-9c8d-f1d55e4c1c1c" xlink:href="apd-20260331.xsd#apd_AmericasSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019c1ff6-d89b-70dc-abdd-f6fa3672a228" xlink:to="loc_apd_AmericasSegmentMember_019c1ff6-d89b-7802-9c8d-f1d55e4c1c1c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_AsiaSegmentMember_019c1ff6-d89b-7960-b7eb-ff127ef411f2" xlink:href="apd-20260331.xsd#apd_AsiaSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019c1ff6-d89b-70dc-abdd-f6fa3672a228" xlink:to="loc_apd_AsiaSegmentMember_019c1ff6-d89b-7960-b7eb-ff127ef411f2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_EuropeSegmentMember_019c1ff6-d89b-7ad0-ad34-fb80be79ac56" xlink:href="apd-20260331.xsd#apd_EuropeSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019c1ff6-d89b-70dc-abdd-f6fa3672a228" xlink:to="loc_apd_EuropeSegmentMember_019c1ff6-d89b-7ad0-ad34-fb80be79ac56" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_MiddleEastAndIndiaSegmentMember_019c1ff6-d89b-7207-891b-bb67e6913e32" xlink:href="apd-20260331.xsd#apd_MiddleEastAndIndiaSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019c1ff6-d89b-70dc-abdd-f6fa3672a228" xlink:to="loc_apd_MiddleEastAndIndiaSegmentMember_019c1ff6-d89b-7207-891b-bb67e6913e32" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateAndOtherMember_019c1ff6-d89b-7cb8-9148-6ad01fc7f4bd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateAndOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019c1ff6-d89b-70dc-abdd-f6fa3672a228" xlink:to="loc_us-gaap_CorporateAndOtherMember_019c1ff6-d89b-7cb8-9148-6ad01fc7f4bd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019c1ff6-d89b-7585-bdf8-d1404fa188a9" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019c1ff6-d89b-7c16-811c-86bdd9da0db0" xlink:to="loc_srt_ConsolidationItemsAxis_019c1ff6-d89b-7585-bdf8-d1404fa188a9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019c1ff6-d89b-7585-bdf8-d1404fa188a9_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019c1ff6-d89b-7585-bdf8-d1404fa188a9" xlink:to="loc_srt_ConsolidationItemsDomain_019c1ff6-d89b-7585-bdf8-d1404fa188a9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019c1ff6-d89b-771e-8fdb-9196fad3917d" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019c1ff6-d89b-7585-bdf8-d1404fa188a9" xlink:to="loc_srt_ConsolidationItemsDomain_019c1ff6-d89b-771e-8fdb-9196fad3917d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019c1ff6-d89b-7d06-9b11-c21b757c1311" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019c1ff6-d89b-771e-8fdb-9196fad3917d" xlink:to="loc_us-gaap_OperatingSegmentsMember_019c1ff6-d89b-7d06-9b11-c21b757c1311" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019c1ff6-d89b-7fb2-a86e-bb242452f1ff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019c1ff6-d89b-7c16-811c-86bdd9da0db0" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019c1ff6-d89b-7fb2-a86e-bb242452f1ff" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019c1ff6-d89b-7fb2-a86e-bb242452f1ff_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019c1ff6-d89b-7fb2-a86e-bb242452f1ff" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019c1ff6-d89b-7fb2-a86e-bb242452f1ff_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019c1ff6-d89b-7c90-b69e-3eb87492cbe5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019c1ff6-d89b-7fb2-a86e-bb242452f1ff" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019c1ff6-d89b-7c90-b69e-3eb87492cbe5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_019c1ff6-d89b-7db1-88cf-3eeb37c18997" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019c1ff6-d89b-7c90-b69e-3eb87492cbe5" xlink:to="loc_us-gaap_SalesRevenueNetMember_019c1ff6-d89b-7db1-88cf-3eeb37c18997" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019c1ff6-d89b-71a3-81f2-11d99da97de5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019c1ff6-d89b-7c16-811c-86bdd9da0db0" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019c1ff6-d89b-71a3-81f2-11d99da97de5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019c1ff6-d89b-71a3-81f2-11d99da97de5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019c1ff6-d89b-71a3-81f2-11d99da97de5" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019c1ff6-d89b-71a3-81f2-11d99da97de5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019c1ff6-d89b-7c8a-a596-2298ce2a17f1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019c1ff6-d89b-71a3-81f2-11d99da97de5" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019c1ff6-d89b-7c8a-a596-2298ce2a17f1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_RevenueSourceConcentrationRiskMember_019c1ff6-d89b-7b49-8ca9-e3acc1bb53f3" xlink:href="apd-20260331.xsd#apd_RevenueSourceConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019c1ff6-d89b-7c8a-a596-2298ce2a17f1" xlink:to="loc_apd_RevenueSourceConcentrationRiskMember_019c1ff6-d89b-7b49-8ca9-e3acc1bb53f3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019c1ff6-d89b-7fba-ac43-cf8908adf3c7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019c1ff6-d89b-792e-9486-63219c57258a" xlink:to="loc_us-gaap_Revenues_019c1ff6-d89b-7fba-ac43-cf8908adf3c7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_PercentSalesSupplyMode_019c1ff6-d89b-72c8-a4df-6ad62caea0f8" xlink:href="apd-20260331.xsd#apd_PercentSalesSupplyMode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019c1ff6-d89b-792e-9486-63219c57258a" xlink:to="loc_apd_PercentSalesSupplyMode_019c1ff6-d89b-72c8-a4df-6ad62caea0f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019c1ff6-d89b-774c-afd7-9eb6d47480f0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019c1ff6-d89b-792e-9486-63219c57258a" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019c1ff6-d89b-774c-afd7-9eb6d47480f0" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/RevenueRecognitionRemainingPerformanceObligationsDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#RevenueRecognitionRemainingPerformanceObligationsDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/RevenueRecognitionRemainingPerformanceObligationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019c1ff6-d89b-7db9-9cc2-c0e28f8d8412" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_019c1ff6-d89b-78fe-99f8-1d0902f5a48e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019c1ff6-d89b-7db9-9cc2-c0e28f8d8412" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_019c1ff6-d89b-78fe-99f8-1d0902f5a48e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_019c1ff6-d89b-7a6d-bc25-9eb68a88b6a4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_019c1ff6-d89b-78fe-99f8-1d0902f5a48e" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_019c1ff6-d89b-7a6d-bc25-9eb68a88b6a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_019c1ff6-d89b-7daa-be40-8921d8d54b10" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019c1ff6-d89b-7db9-9cc2-c0e28f8d8412" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_019c1ff6-d89b-7daa-be40-8921d8d54b10" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019c1ff6-d89b-7cc1-95b5-a13fa29b4b9e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019c1ff6-d89b-7db9-9cc2-c0e28f8d8412" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019c1ff6-d89b-7cc1-95b5-a13fa29b4b9e" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/RevenueRecognitionRemainingPerformanceObligationsDetails_1" xlink:type="simple" xlink:href="apd-20260331.xsd#RevenueRecognitionRemainingPerformanceObligationsDetails_1"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/RevenueRecognitionRemainingPerformanceObligationsDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019c1ff6-d89b-7db9-9cc2-c0e28f8d8412" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_019c1ff6-d89b-78fe-99f8-1d0902f5a48e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019c1ff6-d89b-7db9-9cc2-c0e28f8d8412" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_019c1ff6-d89b-78fe-99f8-1d0902f5a48e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_019c1ff6-d89b-7daa-be40-8921d8d54b10" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019c1ff6-d89b-7db9-9cc2-c0e28f8d8412" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_019c1ff6-d89b-7daa-be40-8921d8d54b10" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019c1ff6-d89b-7cc1-95b5-a13fa29b4b9e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_019c1ff6-d89b-7db9-9cc2-c0e28f8d8412" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_019c1ff6-d89b-7cc1-95b5-a13fa29b4b9e" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/GoodwillScheduleofGoodwillbySegmentDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#GoodwillScheduleofGoodwillbySegmentDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/GoodwillScheduleofGoodwillbySegmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillLineItems_019c1ff6-d89b-73de-8559-c229474493a8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfGoodwillTable_019c1ff6-d89b-70fe-9055-852bb156b8f0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfGoodwillTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_GoodwillLineItems_019c1ff6-d89b-73de-8559-c229474493a8" xlink:to="loc_us-gaap_ScheduleOfGoodwillTable_019c1ff6-d89b-70fe-9055-852bb156b8f0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019c1ff6-d89b-7137-9888-bac6b5541e50" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGoodwillTable_019c1ff6-d89b-70fe-9055-852bb156b8f0" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019c1ff6-d89b-7137-9888-bac6b5541e50" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019c1ff6-d89b-7137-9888-bac6b5541e50_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019c1ff6-d89b-7137-9888-bac6b5541e50" xlink:to="loc_us-gaap_SegmentDomain_019c1ff6-d89b-7137-9888-bac6b5541e50_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019c1ff6-d89b-7ded-bc35-bc9b9d21baae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019c1ff6-d89b-7137-9888-bac6b5541e50" xlink:to="loc_us-gaap_SegmentDomain_019c1ff6-d89b-7ded-bc35-bc9b9d21baae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_AmericasSegmentMember_019c1ff6-d89b-75f2-98a3-f8c6ef57bcc1" xlink:href="apd-20260331.xsd#apd_AmericasSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019c1ff6-d89b-7ded-bc35-bc9b9d21baae" xlink:to="loc_apd_AmericasSegmentMember_019c1ff6-d89b-75f2-98a3-f8c6ef57bcc1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_AsiaSegmentMember_019c1ff6-d89b-702e-86c1-0e425974d48e" xlink:href="apd-20260331.xsd#apd_AsiaSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019c1ff6-d89b-7ded-bc35-bc9b9d21baae" xlink:to="loc_apd_AsiaSegmentMember_019c1ff6-d89b-702e-86c1-0e425974d48e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_EuropeSegmentMember_019c1ff6-d89b-743d-bb9e-2e754194bfba" xlink:href="apd-20260331.xsd#apd_EuropeSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019c1ff6-d89b-7ded-bc35-bc9b9d21baae" xlink:to="loc_apd_EuropeSegmentMember_019c1ff6-d89b-743d-bb9e-2e754194bfba" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_MiddleEastAndIndiaSegmentMember_019c1ff6-d89b-71ca-8ddd-c045136bf795" xlink:href="apd-20260331.xsd#apd_MiddleEastAndIndiaSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019c1ff6-d89b-7ded-bc35-bc9b9d21baae" xlink:to="loc_apd_MiddleEastAndIndiaSegmentMember_019c1ff6-d89b-71ca-8ddd-c045136bf795" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateAndOtherMember_019c1ff6-d89b-7d95-bbc8-8fbe5442e5ab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateAndOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019c1ff6-d89b-7ded-bc35-bc9b9d21baae" xlink:to="loc_us-gaap_CorporateAndOtherMember_019c1ff6-d89b-7d95-bbc8-8fbe5442e5ab" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillRollForward_019c1ff6-d89b-7678-9130-1099f6dfd411" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_019c1ff6-d89b-73de-8559-c229474493a8" xlink:to="loc_us-gaap_GoodwillRollForward_019c1ff6-d89b-7678-9130-1099f6dfd411" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019c1ff6-d89b-7da5-b8cd-a020c88f3d59" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_019c1ff6-d89b-7678-9130-1099f6dfd411" xlink:to="loc_us-gaap_Goodwill_019c1ff6-d89b-7da5-b8cd-a020c88f3d59" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillTranslationAndPurchaseAccountingAdjustments_019c1ff6-d89b-77ce-915f-bf73efbe132f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillTranslationAndPurchaseAccountingAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_019c1ff6-d89b-7678-9130-1099f6dfd411" xlink:to="loc_us-gaap_GoodwillTranslationAndPurchaseAccountingAdjustments_019c1ff6-d89b-77ce-915f-bf73efbe132f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019c1ff6-d89b-7f2f-86d0-de73e748ed9a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Goodwill"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/GoodwillScheduleofAccumulatedImpairmentLossesDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#GoodwillScheduleofAccumulatedImpairmentLossesDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/GoodwillScheduleofAccumulatedImpairmentLossesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillLineItems_019c1ff6-d89b-7c83-a825-3727be4895d2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfGoodwillTable_019c1ff6-d89b-7ff8-bd73-fba033fe7237" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfGoodwillTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_GoodwillLineItems_019c1ff6-d89b-7c83-a825-3727be4895d2" xlink:to="loc_us-gaap_ScheduleOfGoodwillTable_019c1ff6-d89b-7ff8-bd73-fba033fe7237" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019c1ff6-d89b-74ac-9fcc-7ddd4ec25dfa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGoodwillTable_019c1ff6-d89b-7ff8-bd73-fba033fe7237" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019c1ff6-d89b-74ac-9fcc-7ddd4ec25dfa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019c1ff6-d89b-74ac-9fcc-7ddd4ec25dfa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019c1ff6-d89b-74ac-9fcc-7ddd4ec25dfa" xlink:to="loc_us-gaap_SegmentDomain_019c1ff6-d89b-74ac-9fcc-7ddd4ec25dfa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019c1ff6-d89b-77a5-8443-06bea75bb5a1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019c1ff6-d89b-74ac-9fcc-7ddd4ec25dfa" xlink:to="loc_us-gaap_SegmentDomain_019c1ff6-d89b-77a5-8443-06bea75bb5a1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_AmericasSegmentMember_019c1ff6-d89b-792d-955a-61574680239b" xlink:href="apd-20260331.xsd#apd_AmericasSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019c1ff6-d89b-77a5-8443-06bea75bb5a1" xlink:to="loc_apd_AmericasSegmentMember_019c1ff6-d89b-792d-955a-61574680239b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillGross_019c1ff6-d89b-7754-b99b-9d5f66e42f9c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_019c1ff6-d89b-7c83-a825-3727be4895d2" xlink:to="loc_us-gaap_GoodwillGross_019c1ff6-d89b-7754-b99b-9d5f66e42f9c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillImpairedAccumulatedImpairmentLoss_019c1ff6-d89b-78a7-89d7-fd8d05523e57" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillImpairedAccumulatedImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_019c1ff6-d89b-7c83-a825-3727be4895d2" xlink:to="loc_us-gaap_GoodwillImpairedAccumulatedImpairmentLoss_019c1ff6-d89b-78a7-89d7-fd8d05523e57" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019c1ff6-d89b-73d2-a8c1-877ac5ea577c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_019c1ff6-d89b-7c83-a825-3727be4895d2" xlink:to="loc_us-gaap_Goodwill_019c1ff6-d89b-73d2-a8c1-877ac5ea577c" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/FinancialInstrumentsNarrativeDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#FinancialInstrumentsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/FinancialInstrumentsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_019c1ff6-d89b-764f-abb6-42752514372c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_019c1ff6-d89b-7ad9-9ae1-7fd5a0ba0eaf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_019c1ff6-d89b-764f-abb6-42752514372c" xlink:to="loc_us-gaap_DerivativeTable_019c1ff6-d89b-7ad9-9ae1-7fd5a0ba0eaf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7901-beff-6734769ac4c6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019c1ff6-d89b-7ad9-9ae1-7fd5a0ba0eaf" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7901-beff-6734769ac4c6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7901-beff-6734769ac4c6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7901-beff-6734769ac4c6" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7901-beff-6734769ac4c6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-79eb-83c7-8f5d3ffc9dd8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7901-beff-6734769ac4c6" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-79eb-83c7-8f5d3ffc9dd8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForwardContractsMember_019c1ff6-d89b-7da9-acbe-ee6ad1a505f0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForwardContractsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-79eb-83c7-8f5d3ffc9dd8" xlink:to="loc_us-gaap_ForwardContractsMember_019c1ff6-d89b-7da9-acbe-ee6ad1a505f0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCorporateDebtSecuritiesMember_019c1ff6-d89b-7ee0-a035-ab88c11ec3ed" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForeignCorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-79eb-83c7-8f5d3ffc9dd8" xlink:to="loc_us-gaap_ForeignCorporateDebtSecuritiesMember_019c1ff6-d89b-7ee0-a035-ab88c11ec3ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019c1ff6-d89b-7f6c-b860-035f4276635d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019c1ff6-d89b-7ad9-9ae1-7fd5a0ba0eaf" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019c1ff6-d89b-7f6c-b860-035f4276635d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-7f6c-b860-035f4276635d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019c1ff6-d89b-7f6c-b860-035f4276635d" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-7f6c-b860-035f4276635d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-7e5e-a3e9-bf5d0022bae1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019c1ff6-d89b-7f6c-b860-035f4276635d" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-7e5e-a3e9-bf5d0022bae1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_019c1ff6-d89b-7c67-b9e1-6c592fa7cbf7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashFlowHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-7e5e-a3e9-bf5d0022bae1" xlink:to="loc_us-gaap_CashFlowHedgingMember_019c1ff6-d89b-7c67-b9e1-6c592fa7cbf7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_EuroDenominatedMember_019c1ff6-d89b-7112-adfa-a8412c1554a2" xlink:href="apd-20260331.xsd#apd_EuroDenominatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-7e5e-a3e9-bf5d0022bae1" xlink:to="loc_apd_EuroDenominatedMember_019c1ff6-d89b-7112-adfa-a8412c1554a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MaximumRemainingMaturityOfForeignCurrencyDerivatives1_019c1ff6-d89b-7bd3-8941-217dde667cdb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MaximumRemainingMaturityOfForeignCurrencyDerivatives1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019c1ff6-d89b-764f-abb6-42752514372c" xlink:to="loc_us-gaap_MaximumRemainingMaturityOfForeignCurrencyDerivatives1_019c1ff6-d89b-7bd3-8941-217dde667cdb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotionalAmountOfNonderivativeInstruments_019c1ff6-d89b-773c-8df5-b2f2ef2a0a9f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NotionalAmountOfNonderivativeInstruments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019c1ff6-d89b-764f-abb6-42752514372c" xlink:to="loc_us-gaap_NotionalAmountOfNonderivativeInstruments_019c1ff6-d89b-773c-8df5-b2f2ef2a0a9f" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/FinancialInstrumentsCurrencyPriceRiskManagementInstrumentsDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#FinancialInstrumentsCurrencyPriceRiskManagementInstrumentsDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/FinancialInstrumentsCurrencyPriceRiskManagementInstrumentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_019c1ff6-d89b-787e-8a88-802202efcf04" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_019c1ff6-d89b-770d-a2f8-f1f3f08c089a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_019c1ff6-d89b-787e-8a88-802202efcf04" xlink:to="loc_us-gaap_DerivativeTable_019c1ff6-d89b-770d-a2f8-f1f3f08c089a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7671-b62b-085d5cbaf5cd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019c1ff6-d89b-770d-a2f8-f1f3f08c089a" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7671-b62b-085d5cbaf5cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7671-b62b-085d5cbaf5cd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7671-b62b-085d5cbaf5cd" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7671-b62b-085d5cbaf5cd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7463-ac27-c98a1331ffc0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7671-b62b-085d5cbaf5cd" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7463-ac27-c98a1331ffc0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForwardContractsMember_019c1ff6-d89b-721c-abfd-e9c7630f557e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForwardContractsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7463-ac27-c98a1331ffc0" xlink:to="loc_us-gaap_ForwardContractsMember_019c1ff6-d89b-721c-abfd-e9c7630f557e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_019c1ff6-d89b-71c0-b03b-d2d03d285059" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019c1ff6-d89b-770d-a2f8-f1f3f08c089a" xlink:to="loc_us-gaap_HedgingDesignationAxis_019c1ff6-d89b-71c0-b03b-d2d03d285059" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019c1ff6-d89b-71c0-b03b-d2d03d285059_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_019c1ff6-d89b-71c0-b03b-d2d03d285059" xlink:to="loc_us-gaap_HedgingDesignationDomain_019c1ff6-d89b-71c0-b03b-d2d03d285059_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019c1ff6-d89b-7094-8267-09da91b5c230" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_019c1ff6-d89b-71c0-b03b-d2d03d285059" xlink:to="loc_us-gaap_HedgingDesignationDomain_019c1ff6-d89b-7094-8267-09da91b5c230" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019c1ff6-d89b-7ffc-b1fa-323ec8a56f29" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019c1ff6-d89b-7094-8267-09da91b5c230" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019c1ff6-d89b-7ffc-b1fa-323ec8a56f29" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_019c1ff6-d89b-7b63-8be3-8d5a1bde5bf4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NondesignatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019c1ff6-d89b-7094-8267-09da91b5c230" xlink:to="loc_us-gaap_NondesignatedMember_019c1ff6-d89b-7b63-8be3-8d5a1bde5bf4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019c1ff6-d89b-791b-bde2-e32f6dc84c90" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019c1ff6-d89b-770d-a2f8-f1f3f08c089a" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019c1ff6-d89b-791b-bde2-e32f6dc84c90" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-791b-bde2-e32f6dc84c90_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019c1ff6-d89b-791b-bde2-e32f6dc84c90" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-791b-bde2-e32f6dc84c90_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-72b8-82c3-439de3856b69" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019c1ff6-d89b-791b-bde2-e32f6dc84c90" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-72b8-82c3-439de3856b69" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_019c1ff6-d89b-75f8-bd10-82730f1802bf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashFlowHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-72b8-82c3-439de3856b69" xlink:to="loc_us-gaap_CashFlowHedgingMember_019c1ff6-d89b-75f8-bd10-82730f1802bf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetInvestmentHedgingMember_019c1ff6-d89b-7694-9659-1f6da9634bc5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetInvestmentHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-72b8-82c3-439de3856b69" xlink:to="loc_us-gaap_NetInvestmentHedgingMember_019c1ff6-d89b-7694-9659-1f6da9634bc5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_019c1ff6-d89b-7ea2-a386-4a868276771c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019c1ff6-d89b-787e-8a88-802202efcf04" xlink:to="loc_us-gaap_DerivativeNotionalAmount_019c1ff6-d89b-7ea2-a386-4a868276771c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAverageRemainingMaturity1_019c1ff6-d89b-74c1-866a-f5a1261ba2c1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeAverageRemainingMaturity1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019c1ff6-d89b-787e-8a88-802202efcf04" xlink:to="loc_us-gaap_DerivativeAverageRemainingMaturity1_019c1ff6-d89b-74c1-866a-f5a1261ba2c1" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/FinancialInstrumentsInterestRateManagementContractsandCrossCurrencyInterestRateSwapsDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#FinancialInstrumentsInterestRateManagementContractsandCrossCurrencyInterestRateSwapsDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/FinancialInstrumentsInterestRateManagementContractsandCrossCurrencyInterestRateSwapsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_019c1ff6-d89b-795a-aed7-265832bf5b4e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_019c1ff6-d89b-7c66-8307-341e478e1511" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_019c1ff6-d89b-795a-aed7-265832bf5b4e" xlink:to="loc_us-gaap_DerivativeTable_019c1ff6-d89b-7c66-8307-341e478e1511" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-70e1-b78f-2950fb455c86" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019c1ff6-d89b-7c66-8307-341e478e1511" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-70e1-b78f-2950fb455c86" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-70e1-b78f-2950fb455c86_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-70e1-b78f-2950fb455c86" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-70e1-b78f-2950fb455c86_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-72fe-bde3-e148cc0e6f00" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-70e1-b78f-2950fb455c86" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-72fe-bde3-e148cc0e6f00" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_019c1ff6-d89b-7871-a04a-d18cde9dc3c5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-72fe-bde3-e148cc0e6f00" xlink:to="loc_us-gaap_InterestRateSwapMember_019c1ff6-d89b-7871-a04a-d18cde9dc3c5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CrossCurrencyInterestRateContractMember_019c1ff6-d89b-77fd-b10b-cae87734fe92" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CrossCurrencyInterestRateContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-72fe-bde3-e148cc0e6f00" xlink:to="loc_us-gaap_CrossCurrencyInterestRateContractMember_019c1ff6-d89b-77fd-b10b-cae87734fe92" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_019c1ff6-d89b-7564-8b30-0d85cb7ed521" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019c1ff6-d89b-7c66-8307-341e478e1511" xlink:to="loc_us-gaap_HedgingDesignationAxis_019c1ff6-d89b-7564-8b30-0d85cb7ed521" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019c1ff6-d89b-7564-8b30-0d85cb7ed521_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_019c1ff6-d89b-7564-8b30-0d85cb7ed521" xlink:to="loc_us-gaap_HedgingDesignationDomain_019c1ff6-d89b-7564-8b30-0d85cb7ed521_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019c1ff6-d89b-7d50-b2f6-8cf925274031" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_019c1ff6-d89b-7564-8b30-0d85cb7ed521" xlink:to="loc_us-gaap_HedgingDesignationDomain_019c1ff6-d89b-7d50-b2f6-8cf925274031" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019c1ff6-d89b-7787-a04d-0e53380e4ad2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019c1ff6-d89b-7d50-b2f6-8cf925274031" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019c1ff6-d89b-7787-a04d-0e53380e4ad2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_019c1ff6-d89b-7249-8cfd-7327c07cba1a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NondesignatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019c1ff6-d89b-7d50-b2f6-8cf925274031" xlink:to="loc_us-gaap_NondesignatedMember_019c1ff6-d89b-7249-8cfd-7327c07cba1a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019c1ff6-d89b-7a62-8862-c4da92ab95ee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019c1ff6-d89b-7c66-8307-341e478e1511" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019c1ff6-d89b-7a62-8862-c4da92ab95ee" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-7a62-8862-c4da92ab95ee_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019c1ff6-d89b-7a62-8862-c4da92ab95ee" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-7a62-8862-c4da92ab95ee_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-7dfa-86f9-bce9233dcfa0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019c1ff6-d89b-7a62-8862-c4da92ab95ee" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-7dfa-86f9-bce9233dcfa0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueHedgingMember_019c1ff6-d89b-720d-8d47-1b857796f086" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-7dfa-86f9-bce9233dcfa0" xlink:to="loc_us-gaap_FairValueHedgingMember_019c1ff6-d89b-720d-8d47-1b857796f086" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetInvestmentHedgingMember_019c1ff6-d89b-7cb1-890b-0fbc6e203a11" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetInvestmentHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-7dfa-86f9-bce9233dcfa0" xlink:to="loc_us-gaap_NetInvestmentHedgingMember_019c1ff6-d89b-7cb1-890b-0fbc6e203a11" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_019c1ff6-d89b-760f-acc1-2dbee07769ca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashFlowHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-7dfa-86f9-bce9233dcfa0" xlink:to="loc_us-gaap_CashFlowHedgingMember_019c1ff6-d89b-760f-acc1-2dbee07769ca" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_019c1ff6-d89b-743f-8708-623b0e81522a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019c1ff6-d89b-7c66-8307-341e478e1511" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_019c1ff6-d89b-743f-8708-623b0e81522a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_019c1ff6-d89b-743f-8708-623b0e81522a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_019c1ff6-d89b-743f-8708-623b0e81522a" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_019c1ff6-d89b-743f-8708-623b0e81522a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_019c1ff6-d89b-73a5-a539-1601cc4bbad7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_019c1ff6-d89b-743f-8708-623b0e81522a" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_019c1ff6-d89b-73a5-a539-1601cc4bbad7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherOperatingIncomeExpenseMember_019c1ff6-d89b-7a2d-9153-3acba9424cfc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherOperatingIncomeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_019c1ff6-d89b-73a5-a539-1601cc4bbad7" xlink:to="loc_us-gaap_OtherOperatingIncomeExpenseMember_019c1ff6-d89b-7a2d-9153-3acba9424cfc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_019c1ff6-d89b-7fa3-b3bb-fcb8af398596" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019c1ff6-d89b-795a-aed7-265832bf5b4e" xlink:to="loc_us-gaap_DerivativeNotionalAmount_019c1ff6-d89b-7fa3-b3bb-fcb8af398596" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_DerivativeAverageRatePay_019c1ff6-d89b-74a5-8d61-a51f0f01ddb9" xlink:href="apd-20260331.xsd#apd_DerivativeAverageRatePay"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019c1ff6-d89b-795a-aed7-265832bf5b4e" xlink:to="loc_apd_DerivativeAverageRatePay_019c1ff6-d89b-74a5-8d61-a51f0f01ddb9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentVariableInterestRateTypeExtensibleEnumeration_019c1ff6-d89b-7b14-88d5-edd8271df445" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentVariableInterestRateTypeExtensibleEnumeration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019c1ff6-d89b-795a-aed7-265832bf5b4e" xlink:to="loc_us-gaap_DebtInstrumentVariableInterestRateTypeExtensibleEnumeration_019c1ff6-d89b-7b14-88d5-edd8271df445" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_DerivativeAverageRateReceive_019c1ff6-d89b-764c-a0cb-6181ecd8eeef" xlink:href="apd-20260331.xsd#apd_DerivativeAverageRateReceive"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019c1ff6-d89b-795a-aed7-265832bf5b4e" xlink:to="loc_apd_DerivativeAverageRateReceive_019c1ff6-d89b-764c-a0cb-6181ecd8eeef" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_DerivativeDescriptionOfVariableRateBasisReceive_019c1ff6-d89b-7e2a-9260-f95fd216034d" xlink:href="apd-20260331.xsd#apd_DerivativeDescriptionOfVariableRateBasisReceive"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019c1ff6-d89b-795a-aed7-265832bf5b4e" xlink:to="loc_apd_DerivativeDescriptionOfVariableRateBasisReceive_019c1ff6-d89b-7e2a-9260-f95fd216034d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAverageRemainingMaturity1_019c1ff6-d89b-7940-9f94-831955884fee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeAverageRemainingMaturity1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019c1ff6-d89b-795a-aed7-265832bf5b4e" xlink:to="loc_us-gaap_DerivativeAverageRemainingMaturity1_019c1ff6-d89b-7940-9f94-831955884fee" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/FinancialInstrumentsCarryingAmountandCumulativeHedgingAdjustmentDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#FinancialInstrumentsCarryingAmountandCumulativeHedgingAdjustmentDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/FinancialInstrumentsCarryingAmountandCumulativeHedgingAdjustmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019c1ff6-d89b-7a52-a8a8-62e81009f27c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019c1ff6-d89b-7319-a577-0bc60bb38752" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019c1ff6-d89b-7a52-a8a8-62e81009f27c" xlink:to="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019c1ff6-d89b-7319-a577-0bc60bb38752" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_019c1ff6-d89b-703a-ad15-0aa0688d4907" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByLiabilityClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_019c1ff6-d89b-7319-a577-0bc60bb38752" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_019c1ff6-d89b-703a-ad15-0aa0688d4907" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019c1ff6-d89b-703a-ad15-0aa0688d4907_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_019c1ff6-d89b-703a-ad15-0aa0688d4907" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019c1ff6-d89b-703a-ad15-0aa0688d4907_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019c1ff6-d89b-7f78-993c-3f0f5c5d0a8f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_019c1ff6-d89b-703a-ad15-0aa0688d4907" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019c1ff6-d89b-7f78-993c-3f0f5c5d0a8f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_CurrentPortionOfLongTermDebtMember_019c1ff6-d89b-7c8b-8b77-c89a60297429" xlink:href="apd-20260331.xsd#apd_CurrentPortionOfLongTermDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019c1ff6-d89b-7f78-993c-3f0f5c5d0a8f" xlink:to="loc_apd_CurrentPortionOfLongTermDebtMember_019c1ff6-d89b-7c8b-8b77-c89a60297429" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMember_019c1ff6-d89b-7586-9a20-44af2b9d4ff4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019c1ff6-d89b-7f78-993c-3f0f5c5d0a8f" xlink:to="loc_us-gaap_LongTermDebtMember_019c1ff6-d89b-7586-9a20-44af2b9d4ff4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgedLiabilityFairValueHedge_019c1ff6-d89b-70ae-8f4c-070c479ac977" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgedLiabilityFairValueHedge"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019c1ff6-d89b-7a52-a8a8-62e81009f27c" xlink:to="loc_us-gaap_HedgedLiabilityFairValueHedge_019c1ff6-d89b-70ae-8f4c-070c479ac977" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgedLiabilityFairValueHedgeCumulativeIncreaseDecrease_019c1ff6-d89b-7210-b4de-f191a8f49987" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgedLiabilityFairValueHedgeCumulativeIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_019c1ff6-d89b-7a52-a8a8-62e81009f27c" xlink:to="loc_us-gaap_HedgedLiabilityFairValueHedgeCumulativeIncreaseDecrease_019c1ff6-d89b-7210-b4de-f191a8f49987" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/FinancialInstrumentsFairValueandBalanceSheetLocationofDerivativesDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#FinancialInstrumentsFairValueandBalanceSheetLocationofDerivativesDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/FinancialInstrumentsFairValueandBalanceSheetLocationofDerivativesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_019c1ff6-d89b-76d3-b63a-f9b500524a36" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_019c1ff6-d89b-7b51-8939-5aa402727aab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_019c1ff6-d89b-76d3-b63a-f9b500524a36" xlink:to="loc_us-gaap_DerivativeTable_019c1ff6-d89b-7b51-8939-5aa402727aab" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_019c1ff6-d89b-784a-a617-1a1e17f8dfbb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019c1ff6-d89b-7b51-8939-5aa402727aab" xlink:to="loc_us-gaap_HedgingDesignationAxis_019c1ff6-d89b-784a-a617-1a1e17f8dfbb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019c1ff6-d89b-784a-a617-1a1e17f8dfbb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_019c1ff6-d89b-784a-a617-1a1e17f8dfbb" xlink:to="loc_us-gaap_HedgingDesignationDomain_019c1ff6-d89b-784a-a617-1a1e17f8dfbb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019c1ff6-d89b-7df3-a3cf-9cdc4a01a5a6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_019c1ff6-d89b-784a-a617-1a1e17f8dfbb" xlink:to="loc_us-gaap_HedgingDesignationDomain_019c1ff6-d89b-7df3-a3cf-9cdc4a01a5a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019c1ff6-d89b-7c6d-9fd7-6dcd01e6ef61" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019c1ff6-d89b-7df3-a3cf-9cdc4a01a5a6" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019c1ff6-d89b-7c6d-9fd7-6dcd01e6ef61" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_019c1ff6-d89b-7960-b00a-27a43bcb3a0d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NondesignatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019c1ff6-d89b-7df3-a3cf-9cdc4a01a5a6" xlink:to="loc_us-gaap_NondesignatedMember_019c1ff6-d89b-7960-b00a-27a43bcb3a0d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_019c1ff6-d89b-7648-8bb6-bb1ffc2bf27e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019c1ff6-d89b-7b51-8939-5aa402727aab" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_019c1ff6-d89b-7648-8bb6-bb1ffc2bf27e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_019c1ff6-d89b-7648-8bb6-bb1ffc2bf27e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_019c1ff6-d89b-7648-8bb6-bb1ffc2bf27e" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_019c1ff6-d89b-7648-8bb6-bb1ffc2bf27e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_019c1ff6-d89b-73a2-affe-c779c1dfedba" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_019c1ff6-d89b-7648-8bb6-bb1ffc2bf27e" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_019c1ff6-d89b-73a2-affe-c779c1dfedba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCurrentAssetsMember_019c1ff6-d89b-7a93-87cf-1358f5d78e66" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherCurrentAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_019c1ff6-d89b-73a2-affe-c779c1dfedba" xlink:to="loc_us-gaap_OtherCurrentAssetsMember_019c1ff6-d89b-7a93-87cf-1358f5d78e66" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNoncurrentAssetsMember_019c1ff6-d89b-7d96-a6ef-f35caf63f3c0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherNoncurrentAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_019c1ff6-d89b-73a2-affe-c779c1dfedba" xlink:to="loc_us-gaap_OtherNoncurrentAssetsMember_019c1ff6-d89b-7d96-a6ef-f35caf63f3c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesMember_019c1ff6-d89b-775e-8fdc-2d59cf44e7bd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccruedLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_019c1ff6-d89b-73a2-affe-c779c1dfedba" xlink:to="loc_us-gaap_AccruedLiabilitiesMember_019c1ff6-d89b-775e-8fdc-2d59cf44e7bd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNoncurrentLiabilitiesMember_019c1ff6-d89b-7b6e-8a6e-5a46db02911b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherNoncurrentLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_019c1ff6-d89b-73a2-affe-c779c1dfedba" xlink:to="loc_us-gaap_OtherNoncurrentLiabilitiesMember_019c1ff6-d89b-7b6e-8a6e-5a46db02911b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7af8-ac76-2acfe2abedfc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019c1ff6-d89b-7b51-8939-5aa402727aab" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7af8-ac76-2acfe2abedfc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7af8-ac76-2acfe2abedfc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7af8-ac76-2acfe2abedfc" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7af8-ac76-2acfe2abedfc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-739e-96ba-21d66f6ddb5a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7af8-ac76-2acfe2abedfc" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-739e-96ba-21d66f6ddb5a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForwardContractsMember_019c1ff6-d89b-733e-ae36-9366a457a2fa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForwardContractsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-739e-96ba-21d66f6ddb5a" xlink:to="loc_us-gaap_ForwardContractsMember_019c1ff6-d89b-733e-ae36-9366a457a2fa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateContractMember_019c1ff6-d89b-7ba3-9851-f5f99b334281" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-739e-96ba-21d66f6ddb5a" xlink:to="loc_us-gaap_InterestRateContractMember_019c1ff6-d89b-7ba3-9851-f5f99b334281" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_019c1ff6-d89b-7554-a3ae-1fd63ac9f4dc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeFairValueOfDerivativeAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019c1ff6-d89b-76d3-b63a-f9b500524a36" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_019c1ff6-d89b-7554-a3ae-1fd63ac9f4dc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeLiability_019c1ff6-d89b-72b3-b47f-c0f12136056e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeFairValueOfDerivativeLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019c1ff6-d89b-76d3-b63a-f9b500524a36" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeLiability_019c1ff6-d89b-72b3-b47f-c0f12136056e" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/FinancialInstrumentsGainsandLossesRecognizedInOtherComprehensiveIncomeDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#FinancialInstrumentsGainsandLossesRecognizedInOtherComprehensiveIncomeDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/FinancialInstrumentsGainsandLossesRecognizedInOtherComprehensiveIncomeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019c1ff6-d89b-77f5-aaae-e00b92725e06" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsGainLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019c1ff6-d89b-7e8f-8837-d042fcfe2672" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019c1ff6-d89b-77f5-aaae-e00b92725e06" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019c1ff6-d89b-7e8f-8837-d042fcfe2672" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019c1ff6-d89b-704e-915b-e91f7906aebb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019c1ff6-d89b-7e8f-8837-d042fcfe2672" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019c1ff6-d89b-704e-915b-e91f7906aebb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-704e-915b-e91f7906aebb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019c1ff6-d89b-704e-915b-e91f7906aebb" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-704e-915b-e91f7906aebb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-7082-b89f-3734a5fa1a78" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019c1ff6-d89b-704e-915b-e91f7906aebb" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-7082-b89f-3734a5fa1a78" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetInvestmentHedgingMember_019c1ff6-d89b-7fd9-9d11-7da88a456c3c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetInvestmentHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-7082-b89f-3734a5fa1a78" xlink:to="loc_us-gaap_NetInvestmentHedgingMember_019c1ff6-d89b-7fd9-9d11-7da88a456c3c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_019c1ff6-d89b-78e1-aec5-a7222f89b9db" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashFlowHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-7082-b89f-3734a5fa1a78" xlink:to="loc_us-gaap_CashFlowHedgingMember_019c1ff6-d89b-78e1-aec5-a7222f89b9db" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7177-babd-61ff386794e8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019c1ff6-d89b-7e8f-8837-d042fcfe2672" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7177-babd-61ff386794e8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7177-babd-61ff386794e8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7177-babd-61ff386794e8" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7177-babd-61ff386794e8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-79d3-836b-0ddba407f1dd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7177-babd-61ff386794e8" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-79d3-836b-0ddba407f1dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForwardContractsMember_019c1ff6-d89b-722c-837f-a6c7f7d96ec6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForwardContractsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-79d3-836b-0ddba407f1dd" xlink:to="loc_us-gaap_ForwardContractsMember_019c1ff6-d89b-722c-837f-a6c7f7d96ec6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_ForwardContractsExcludedComponentMember_019c1ff6-d89b-739b-a134-c4e5d0394553" xlink:href="apd-20260331.xsd#apd_ForwardContractsExcludedComponentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-79d3-836b-0ddba407f1dd" xlink:to="loc_apd_ForwardContractsExcludedComponentMember_019c1ff6-d89b-739b-a134-c4e5d0394553" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCorporateDebtSecuritiesMember_019c1ff6-d89b-73f1-9fe9-e6adb4a6626d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForeignCorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-79d3-836b-0ddba407f1dd" xlink:to="loc_us-gaap_ForeignCorporateDebtSecuritiesMember_019c1ff6-d89b-73f1-9fe9-e6adb4a6626d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CrossCurrencyInterestRateContractMember_019c1ff6-d89b-7bb4-8d8b-da7f1e103ac4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CrossCurrencyInterestRateContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-79d3-836b-0ddba407f1dd" xlink:to="loc_us-gaap_CrossCurrencyInterestRateContractMember_019c1ff6-d89b-7bb4-8d8b-da7f1e103ac4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherContractMember_019c1ff6-d89b-7c53-b2f8-236be7d17ae6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-79d3-836b-0ddba407f1dd" xlink:to="loc_us-gaap_OtherContractMember_019c1ff6-d89b-7c53-b2f8-236be7d17ae6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SummaryOfNetInvestmentHedgeActivityAbstract_019c1ff6-d89b-743f-b39b-f2f73e6012f7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SummaryOfNetInvestmentHedgeActivityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019c1ff6-d89b-77f5-aaae-e00b92725e06" xlink:to="loc_us-gaap_SummaryOfNetInvestmentHedgeActivityAbstract_019c1ff6-d89b-743f-b39b-f2f73e6012f7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetInvestmentHedgeGainLossBeforeReclassificationAndTax_019c1ff6-d89b-77ff-922c-78e5099e5831" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossNetInvestmentHedgeGainLossBeforeReclassificationAndTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfNetInvestmentHedgeActivityAbstract_019c1ff6-d89b-743f-b39b-f2f73e6012f7" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetInvestmentHedgeGainLossBeforeReclassificationAndTax_019c1ff6-d89b-77ff-922c-78e5099e5831" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTranslationGainLossArisingDuringPeriodTax_019c1ff6-d89b-754b-90d8-f682e27e986c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeForeignCurrencyTranslationGainLossArisingDuringPeriodTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfNetInvestmentHedgeActivityAbstract_019c1ff6-d89b-743f-b39b-f2f73e6012f7" xlink:to="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTranslationGainLossArisingDuringPeriodTax_019c1ff6-d89b-754b-90d8-f682e27e986c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax_019c1ff6-d89b-708b-9948-ce947cb5505b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfNetInvestmentHedgeActivityAbstract_019c1ff6-d89b-743f-b39b-f2f73e6012f7" xlink:to="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax_019c1ff6-d89b-708b-9948-ce947cb5505b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SummaryOfCashFlowHedgeActivityAbstract_019c1ff6-d89b-7b5d-90e5-994c43303f42" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SummaryOfCashFlowHedgeActivityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019c1ff6-d89b-77f5-aaae-e00b92725e06" xlink:to="loc_us-gaap_SummaryOfCashFlowHedgeActivityAbstract_019c1ff6-d89b-7b5d-90e5-994c43303f42" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAndTax_019c1ff6-d89b-7578-921a-befa83fc138e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAndTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfCashFlowHedgeActivityAbstract_019c1ff6-d89b-7b5d-90e5-994c43303f42" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAndTax_019c1ff6-d89b-7578-921a-befa83fc138e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossDerivativeExcludedComponentIncreaseDecreaseBeforeAdjustmentsAndTax_019c1ff6-d89b-7505-9717-593dbc8277a4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossDerivativeExcludedComponentIncreaseDecreaseBeforeAdjustmentsAndTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfCashFlowHedgeActivityAbstract_019c1ff6-d89b-7b5d-90e5-994c43303f42" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossDerivativeExcludedComponentIncreaseDecreaseBeforeAdjustmentsAndTax_019c1ff6-d89b-7505-9717-593dbc8277a4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationTax_019c1ff6-d89b-765a-8992-64a09bbe62cb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfCashFlowHedgeActivityAbstract_019c1ff6-d89b-7b5d-90e5-994c43303f42" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationTax_019c1ff6-d89b-765a-8992-64a09bbe62cb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAfterTax_019c1ff6-d89b-7606-ba21-27e5fe8c3f9f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfCashFlowHedgeActivityAbstract_019c1ff6-d89b-7b5d-90e5-994c43303f42" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAfterTax_019c1ff6-d89b-7606-ba21-27e5fe8c3f9f" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/FinancialInstrumentsCashFlowandFairValueHedgesLocationandAmountsRecognizedDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#FinancialInstrumentsCashFlowandFairValueHedgesLocationandAmountsRecognizedDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/FinancialInstrumentsCashFlowandFairValueHedgesLocationandAmountsRecognizedDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_019c1ff6-d89b-77f8-a96c-5a349c0fec63" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_019c1ff6-d89b-7fca-8f4a-40cdb7e6512b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_019c1ff6-d89b-77f8-a96c-5a349c0fec63" xlink:to="loc_us-gaap_DerivativeTable_019c1ff6-d89b-7fca-8f4a-40cdb7e6512b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019c1ff6-d89b-7ae5-b3df-9bf600a12d1d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019c1ff6-d89b-7fca-8f4a-40cdb7e6512b" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019c1ff6-d89b-7ae5-b3df-9bf600a12d1d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-7ae5-b3df-9bf600a12d1d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019c1ff6-d89b-7ae5-b3df-9bf600a12d1d" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-7ae5-b3df-9bf600a12d1d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-7b83-b88b-04353bca3bb4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019c1ff6-d89b-7ae5-b3df-9bf600a12d1d" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-7b83-b88b-04353bca3bb4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_019c1ff6-d89b-71e7-9d55-0d2ad2374073" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashFlowHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-7b83-b88b-04353bca3bb4" xlink:to="loc_us-gaap_CashFlowHedgingMember_019c1ff6-d89b-71e7-9d55-0d2ad2374073" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueHedgingMember_019c1ff6-d89b-7e6d-bfac-22d328dc0acc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019c1ff6-d89b-7b83-b88b-04353bca3bb4" xlink:to="loc_us-gaap_FairValueHedgingMember_019c1ff6-d89b-7e6d-bfac-22d328dc0acc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7cf1-b12c-540e12c3b96a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019c1ff6-d89b-7fca-8f4a-40cdb7e6512b" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7cf1-b12c-540e12c3b96a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7cf1-b12c-540e12c3b96a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7cf1-b12c-540e12c3b96a" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7cf1-b12c-540e12c3b96a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7ddb-b2a8-9e54c35328ea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7cf1-b12c-540e12c3b96a" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7ddb-b2a8-9e54c35328ea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForwardContractsMember_019c1ff6-d89b-7645-8e81-626b152af5d7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForwardContractsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7ddb-b2a8-9e54c35328ea" xlink:to="loc_us-gaap_ForwardContractsMember_019c1ff6-d89b-7645-8e81-626b152af5d7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_ForwardContractsExcludedComponentMember_019c1ff6-d89b-7e97-b10c-9a9ad92e2275" xlink:href="apd-20260331.xsd#apd_ForwardContractsExcludedComponentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7ddb-b2a8-9e54c35328ea" xlink:to="loc_apd_ForwardContractsExcludedComponentMember_019c1ff6-d89b-7e97-b10c-9a9ad92e2275" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherContractMember_019c1ff6-d89b-7f0f-8476-1e93b05c1374" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7ddb-b2a8-9e54c35328ea" xlink:to="loc_us-gaap_OtherContractMember_019c1ff6-d89b-7f0f-8476-1e93b05c1374" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_019c1ff6-d89b-7302-a6fb-bc6925d51185" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019c1ff6-d89b-7fca-8f4a-40cdb7e6512b" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_019c1ff6-d89b-7302-a6fb-bc6925d51185" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_019c1ff6-d89b-7302-a6fb-bc6925d51185_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_019c1ff6-d89b-7302-a6fb-bc6925d51185" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_019c1ff6-d89b-7302-a6fb-bc6925d51185_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_019c1ff6-d89b-72f8-92fa-132803350980" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_019c1ff6-d89b-7302-a6fb-bc6925d51185" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_019c1ff6-d89b-72f8-92fa-132803350980" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesMember_019c1ff6-d89b-77da-977e-d29e3e079bc9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_019c1ff6-d89b-72f8-92fa-132803350980" xlink:to="loc_us-gaap_SalesMember_019c1ff6-d89b-77da-977e-d29e3e079bc9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_019c1ff6-d89b-7963-bdff-c3b617a31ccc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_019c1ff6-d89b-72f8-92fa-132803350980" xlink:to="loc_us-gaap_CostOfSalesMember_019c1ff6-d89b-7963-bdff-c3b617a31ccc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherOperatingIncomeExpenseMember_019c1ff6-d89b-763b-91c8-38d7d85f3990" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherOperatingIncomeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_019c1ff6-d89b-72f8-92fa-132803350980" xlink:to="loc_us-gaap_OtherOperatingIncomeExpenseMember_019c1ff6-d89b-763b-91c8-38d7d85f3990" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseMember_019c1ff6-d89b-786f-9ae8-79164b9616b8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_019c1ff6-d89b-72f8-92fa-132803350980" xlink:to="loc_us-gaap_InterestExpenseMember_019c1ff6-d89b-786f-9ae8-79164b9616b8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpenseMember_019c1ff6-d89b-7221-8363-08eeb5883947" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherNonoperatingIncomeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_019c1ff6-d89b-72f8-92fa-132803350980" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpenseMember_019c1ff6-d89b-7221-8363-08eeb5883947" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementRelatedDisclosuresAbstract_019c1ff6-d89b-7dac-b384-9c72ec68d644" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementRelatedDisclosuresAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019c1ff6-d89b-77f8-a96c-5a349c0fec63" xlink:to="loc_us-gaap_IncomeStatementRelatedDisclosuresAbstract_019c1ff6-d89b-7dac-b384-9c72ec68d644" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019c1ff6-d89b-7480-9ef7-dbba8e5f8026" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementRelatedDisclosuresAbstract_019c1ff6-d89b-7dac-b384-9c72ec68d644" xlink:to="loc_us-gaap_Revenues_019c1ff6-d89b-7480-9ef7-dbba8e5f8026" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_019c1ff6-d89b-721d-80c6-3f9ce3e16f3f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementRelatedDisclosuresAbstract_019c1ff6-d89b-7dac-b384-9c72ec68d644" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_019c1ff6-d89b-721d-80c6-3f9ce3e16f3f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating_019c1ff6-d89b-70c4-89dc-a81e53a1f426" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestExpenseNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementRelatedDisclosuresAbstract_019c1ff6-d89b-7dac-b384-9c72ec68d644" xlink:to="loc_us-gaap_InterestExpenseNonoperating_019c1ff6-d89b-70c4-89dc-a81e53a1f426" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_019c1ff6-d89b-7ceb-9a8d-bcc34be65141" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementRelatedDisclosuresAbstract_019c1ff6-d89b-7dac-b384-9c72ec68d644" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_019c1ff6-d89b-7ceb-9a8d-bcc34be65141" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectOfCashFlowHedgesOnResultsOfOperationsAbstract_019c1ff6-d89b-7fdb-97bb-da81315a965f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectOfCashFlowHedgesOnResultsOfOperationsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019c1ff6-d89b-77f8-a96c-5a349c0fec63" xlink:to="loc_us-gaap_EffectOfCashFlowHedgesOnResultsOfOperationsAbstract_019c1ff6-d89b-7fdb-97bb-da81315a965f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationBeforeTax_019c1ff6-d89b-7d5a-ac37-e99f3d5f2595" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectOfCashFlowHedgesOnResultsOfOperationsAbstract_019c1ff6-d89b-7fdb-97bb-da81315a965f" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationBeforeTax_019c1ff6-d89b-7d5a-ac37-e99f3d5f2595" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossDerivativeExcludedComponentIncreaseDecreaseAdjustmentsBeforeTax_019c1ff6-d89b-73a9-837e-4eb31e5aac5b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossDerivativeExcludedComponentIncreaseDecreaseAdjustmentsBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectOfCashFlowHedgesOnResultsOfOperationsAbstract_019c1ff6-d89b-7fdb-97bb-da81315a965f" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossDerivativeExcludedComponentIncreaseDecreaseAdjustmentsBeforeTax_019c1ff6-d89b-73a9-837e-4eb31e5aac5b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationTax_019c1ff6-d89b-72b9-83c7-edf78c40ecd6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectOfCashFlowHedgesOnResultsOfOperationsAbstract_019c1ff6-d89b-7fdb-97bb-da81315a965f" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationTax_019c1ff6-d89b-72b9-83c7-edf78c40ecd6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_019c1ff6-d89b-7c38-a372-a55d236f8904" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectOfCashFlowHedgesOnResultsOfOperationsAbstract_019c1ff6-d89b-7fdb-97bb-da81315a965f" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_019c1ff6-d89b-7c38-a372-a55d236f8904" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectOfFairValueHedgesOnResultsOfOperationsAbstract_019c1ff6-d89b-7fca-af50-c50010b94941" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectOfFairValueHedgesOnResultsOfOperationsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019c1ff6-d89b-77f8-a96c-5a349c0fec63" xlink:to="loc_us-gaap_EffectOfFairValueHedgesOnResultsOfOperationsAbstract_019c1ff6-d89b-7fca-af50-c50010b94941" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ChangeInUnrealizedGainLossOnHedgedItemInFairValueHedge1_019c1ff6-d89b-794d-960e-2f055f36583f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ChangeInUnrealizedGainLossOnHedgedItemInFairValueHedge1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectOfFairValueHedgesOnResultsOfOperationsAbstract_019c1ff6-d89b-7fca-af50-c50010b94941" xlink:to="loc_us-gaap_ChangeInUnrealizedGainLossOnHedgedItemInFairValueHedge1_019c1ff6-d89b-794d-960e-2f055f36583f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ChangeInUnrealizedGainLossOnFairValueHedgingInstruments1_019c1ff6-d89b-7440-9612-55f0847aba87" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ChangeInUnrealizedGainLossOnFairValueHedgingInstruments1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectOfFairValueHedgesOnResultsOfOperationsAbstract_019c1ff6-d89b-7fca-af50-c50010b94941" xlink:to="loc_us-gaap_ChangeInUnrealizedGainLossOnFairValueHedgingInstruments1_019c1ff6-d89b-7440-9612-55f0847aba87" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnFairValueHedgesRecognizedInEarnings_019c1ff6-d89b-793c-a5c7-a26a1866a219" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GainLossOnFairValueHedgesRecognizedInEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectOfFairValueHedgesOnResultsOfOperationsAbstract_019c1ff6-d89b-7fca-af50-c50010b94941" xlink:to="loc_us-gaap_GainLossOnFairValueHedgesRecognizedInEarnings_019c1ff6-d89b-793c-a5c7-a26a1866a219" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/FinancialInstrumentsEffectsofDerivativesNotDesignatedasaHedgingInstrumentDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#FinancialInstrumentsEffectsofDerivativesNotDesignatedasaHedgingInstrumentDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/FinancialInstrumentsEffectsofDerivativesNotDesignatedasaHedgingInstrumentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019c1ff6-d89b-7854-8f5c-dc1977a82a34" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsGainLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019c1ff6-d89b-7285-b0e6-fc3fa78b300e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019c1ff6-d89b-7854-8f5c-dc1977a82a34" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019c1ff6-d89b-7285-b0e6-fc3fa78b300e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_019c1ff6-d89b-7776-ab69-4e0f7df4db0a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019c1ff6-d89b-7285-b0e6-fc3fa78b300e" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_019c1ff6-d89b-7776-ab69-4e0f7df4db0a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_019c1ff6-d89b-7776-ab69-4e0f7df4db0a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_019c1ff6-d89b-7776-ab69-4e0f7df4db0a" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_019c1ff6-d89b-7776-ab69-4e0f7df4db0a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_019c1ff6-d89b-7d10-a91b-240a63fd0d17" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_019c1ff6-d89b-7776-ab69-4e0f7df4db0a" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_019c1ff6-d89b-7d10-a91b-240a63fd0d17" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherOperatingIncomeExpenseMember_019c1ff6-d89b-7354-8d5c-97c3301f38e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherOperatingIncomeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_019c1ff6-d89b-7d10-a91b-240a63fd0d17" xlink:to="loc_us-gaap_OtherOperatingIncomeExpenseMember_019c1ff6-d89b-7354-8d5c-97c3301f38e1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpenseMember_019c1ff6-d89b-7713-a0c8-25893c5e5b4b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherNonoperatingIncomeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_019c1ff6-d89b-7d10-a91b-240a63fd0d17" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpenseMember_019c1ff6-d89b-7713-a0c8-25893c5e5b4b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-700a-b035-28a581f06df1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019c1ff6-d89b-7285-b0e6-fc3fa78b300e" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-700a-b035-28a581f06df1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-700a-b035-28a581f06df1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-700a-b035-28a581f06df1" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-700a-b035-28a581f06df1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7c94-a0fe-618bb2683f33" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-700a-b035-28a581f06df1" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7c94-a0fe-618bb2683f33" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForwardContractsMember_019c1ff6-d89b-764a-80d6-e2a19de59a4c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForwardContractsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7c94-a0fe-618bb2683f33" xlink:to="loc_us-gaap_ForwardContractsMember_019c1ff6-d89b-764a-80d6-e2a19de59a4c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_DeDesignatedInterestRateSwapsMember_019c1ff6-d89b-7137-a648-a17d34af9596" xlink:href="apd-20260331.xsd#apd_DeDesignatedInterestRateSwapsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7c94-a0fe-618bb2683f33" xlink:to="loc_apd_DeDesignatedInterestRateSwapsMember_019c1ff6-d89b-7137-a648-a17d34af9596" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherContractMember_019c1ff6-d89b-7a8a-8ee5-91bfe27bdfeb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7c94-a0fe-618bb2683f33" xlink:to="loc_us-gaap_OtherContractMember_019c1ff6-d89b-7a8a-8ee5-91bfe27bdfeb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_019c1ff6-d89b-75dc-aeec-bc843915c61f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_019c1ff6-d89b-7285-b0e6-fc3fa78b300e" xlink:to="loc_us-gaap_HedgingDesignationAxis_019c1ff6-d89b-75dc-aeec-bc843915c61f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019c1ff6-d89b-75dc-aeec-bc843915c61f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_019c1ff6-d89b-75dc-aeec-bc843915c61f" xlink:to="loc_us-gaap_HedgingDesignationDomain_019c1ff6-d89b-75dc-aeec-bc843915c61f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019c1ff6-d89b-7ab3-b752-43128abbfa32" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_019c1ff6-d89b-75dc-aeec-bc843915c61f" xlink:to="loc_us-gaap_HedgingDesignationDomain_019c1ff6-d89b-7ab3-b752-43128abbfa32" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_019c1ff6-d89b-7972-a79b-083fc0267a3d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NondesignatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019c1ff6-d89b-7ab3-b752-43128abbfa32" xlink:to="loc_us-gaap_NondesignatedMember_019c1ff6-d89b-7972-a79b-083fc0267a3d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeGainLossOnDerivativeNet_019c1ff6-d89b-73c3-aee2-3492c02895a5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeGainLossOnDerivativeNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_019c1ff6-d89b-7854-8f5c-dc1977a82a34" xlink:to="loc_us-gaap_DerivativeGainLossOnDerivativeNet_019c1ff6-d89b-73c3-aee2-3492c02895a5" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/FairValueMeasurementsScheduleoftheCarryingValuesandFairValuesofFinancialInstrumentsDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#FairValueMeasurementsScheduleoftheCarryingValuesandFairValuesofFinancialInstrumentsDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/FairValueMeasurementsScheduleoftheCarryingValuesandFairValuesofFinancialInstrumentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019c1ff6-d89b-768c-af11-0493c1c5132d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019c1ff6-d89b-7145-bed9-d57b2fb91163" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByBalanceSheetGroupingTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019c1ff6-d89b-768c-af11-0493c1c5132d" xlink:to="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019c1ff6-d89b-7145-bed9-d57b2fb91163" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7dd4-912a-e0599de3a41e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019c1ff6-d89b-7145-bed9-d57b2fb91163" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7dd4-912a-e0599de3a41e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7dd4-912a-e0599de3a41e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7dd4-912a-e0599de3a41e" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7dd4-912a-e0599de3a41e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-73a0-a2b8-f2cbf582f41e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7dd4-912a-e0599de3a41e" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-73a0-a2b8-f2cbf582f41e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForwardContractsMember_019c1ff6-d89b-7e79-95f0-d5da77a7f2e6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForwardContractsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-73a0-a2b8-f2cbf582f41e" xlink:to="loc_us-gaap_ForwardContractsMember_019c1ff6-d89b-7e79-95f0-d5da77a7f2e6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateContractMember_019c1ff6-d89b-7e95-978e-15590dd6f546" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-73a0-a2b8-f2cbf582f41e" xlink:to="loc_us-gaap_InterestRateContractMember_019c1ff6-d89b-7e95-978e-15590dd6f546" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_019c1ff6-d89b-742c-9911-3803c5ee98c1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019c1ff6-d89b-7145-bed9-d57b2fb91163" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_019c1ff6-d89b-742c-9911-3803c5ee98c1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019c1ff6-d89b-742c-9911-3803c5ee98c1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019c1ff6-d89b-742c-9911-3803c5ee98c1" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019c1ff6-d89b-742c-9911-3803c5ee98c1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019c1ff6-d89b-707f-8dc2-3e7c5343ee35" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019c1ff6-d89b-742c-9911-3803c5ee98c1" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019c1ff6-d89b-707f-8dc2-3e7c5343ee35" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019c1ff6-d89b-71f7-8731-0122f201c52d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019c1ff6-d89b-707f-8dc2-3e7c5343ee35" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019c1ff6-d89b-71f7-8731-0122f201c52d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_019c1ff6-d89b-75ce-94e9-77da937d6a74" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019c1ff6-d89b-707f-8dc2-3e7c5343ee35" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_019c1ff6-d89b-75ce-94e9-77da937d6a74" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019c1ff6-d89b-73be-b60c-deb453c6d894" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019c1ff6-d89b-707f-8dc2-3e7c5343ee35" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019c1ff6-d89b-73be-b60c-deb453c6d894" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssets_019c1ff6-d89b-76a4-9ad0-1c455ca0b794" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019c1ff6-d89b-768c-af11-0493c1c5132d" xlink:to="loc_us-gaap_DerivativeAssets_019c1ff6-d89b-76a4-9ad0-1c455ca0b794" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilities_019c1ff6-d89b-7e68-99c7-63f15ac2ef66" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019c1ff6-d89b-768c-af11-0493c1c5132d" xlink:to="loc_us-gaap_DerivativeLiabilities_019c1ff6-d89b-7e68-99c7-63f15ac2ef66" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019c1ff6-d89b-7c27-8553-32d7e5bbecc7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019c1ff6-d89b-768c-af11-0493c1c5132d" xlink:to="loc_us-gaap_LongTermDebt_019c1ff6-d89b-7c27-8553-32d7e5bbecc7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtFairValue_019c1ff6-d89b-7742-8919-8a2d667485bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019c1ff6-d89b-768c-af11-0493c1c5132d" xlink:to="loc_us-gaap_LongTermDebtFairValue_019c1ff6-d89b-7742-8919-8a2d667485bc" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/FairValueMeasurementsScheduleofRecurringFairValueMeasurementsDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#FairValueMeasurementsScheduleofRecurringFairValueMeasurementsDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/FairValueMeasurementsScheduleofRecurringFairValueMeasurementsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019c1ff6-d89b-7bb5-9880-bff966af01b7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019c1ff6-d89b-7b7f-be91-ed228b0af4af" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByBalanceSheetGroupingTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019c1ff6-d89b-7bb5-9880-bff966af01b7" xlink:to="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019c1ff6-d89b-7b7f-be91-ed228b0af4af" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019c1ff6-d89b-7688-bb97-b121903e1ef2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019c1ff6-d89b-7b7f-be91-ed228b0af4af" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019c1ff6-d89b-7688-bb97-b121903e1ef2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019c1ff6-d89b-7688-bb97-b121903e1ef2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019c1ff6-d89b-7688-bb97-b121903e1ef2" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019c1ff6-d89b-7688-bb97-b121903e1ef2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019c1ff6-d89b-7245-acd7-7ada4c7d0283" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019c1ff6-d89b-7688-bb97-b121903e1ef2" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019c1ff6-d89b-7245-acd7-7ada4c7d0283" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_019c1ff6-d89b-793a-9f47-267b0e9fe2a5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_019c1ff6-d89b-7245-acd7-7ada4c7d0283" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_019c1ff6-d89b-793a-9f47-267b0e9fe2a5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7c8c-a521-36cd9f2d510a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019c1ff6-d89b-7b7f-be91-ed228b0af4af" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7c8c-a521-36cd9f2d510a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7c8c-a521-36cd9f2d510a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7c8c-a521-36cd9f2d510a" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7c8c-a521-36cd9f2d510a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7ae8-916b-54a9e49bb30e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019c1ff6-d89b-7c8c-a521-36cd9f2d510a" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7ae8-916b-54a9e49bb30e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForwardContractsMember_019c1ff6-d89b-715a-bb14-a4facd11f104" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForwardContractsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7ae8-916b-54a9e49bb30e" xlink:to="loc_us-gaap_ForwardContractsMember_019c1ff6-d89b-715a-bb14-a4facd11f104" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateContractMember_019c1ff6-d89b-7435-a22c-9eacb007ca49" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019c1ff6-d89b-7ae8-916b-54a9e49bb30e" xlink:to="loc_us-gaap_InterestRateContractMember_019c1ff6-d89b-7435-a22c-9eacb007ca49" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019c1ff6-d89b-781d-b27d-d0227d5d00f1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019c1ff6-d89b-7b7f-be91-ed228b0af4af" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019c1ff6-d89b-781d-b27d-d0227d5d00f1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019c1ff6-d89b-781d-b27d-d0227d5d00f1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019c1ff6-d89b-781d-b27d-d0227d5d00f1" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019c1ff6-d89b-781d-b27d-d0227d5d00f1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019c1ff6-d89b-738f-8c2a-b242704d9f20" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019c1ff6-d89b-781d-b27d-d0227d5d00f1" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019c1ff6-d89b-738f-8c2a-b242704d9f20" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019c1ff6-d89b-7de3-b342-be0f675e6f86" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019c1ff6-d89b-738f-8c2a-b242704d9f20" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019c1ff6-d89b-7de3-b342-be0f675e6f86" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019c1ff6-d89b-737a-b1c5-e77027614fa0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019c1ff6-d89b-738f-8c2a-b242704d9f20" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019c1ff6-d89b-737a-b1c5-e77027614fa0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019c1ff6-d89b-79a0-be55-5da2b6ac7462" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019c1ff6-d89b-738f-8c2a-b242704d9f20" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019c1ff6-d89b-79a0-be55-5da2b6ac7462" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssets_019c1ff6-d89b-7b58-816e-0090b32982c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019c1ff6-d89b-7bb5-9880-bff966af01b7" xlink:to="loc_us-gaap_DerivativeAssets_019c1ff6-d89b-7b58-816e-0090b32982c2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_019c1ff6-d89b-70cb-bf37-4d53f8d60b29" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019c1ff6-d89b-7bb5-9880-bff966af01b7" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_019c1ff6-d89b-70cb-bf37-4d53f8d60b29" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilities_019c1ff6-d89b-70e2-9a44-62172b584bd0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019c1ff6-d89b-7bb5-9880-bff966af01b7" xlink:to="loc_us-gaap_DerivativeLiabilities_019c1ff6-d89b-70e2-9a44-62172b584bd0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosure_019c1ff6-d89b-7cd9-88b5-f583a44b9084" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019c1ff6-d89b-7bb5-9880-bff966af01b7" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosure_019c1ff6-d89b-7cd9-88b5-f583a44b9084" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/FairValueMeasurementsScheduleofNonrecurringFairValueMeasurementsDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#FairValueMeasurementsScheduleofNonrecurringFairValueMeasurementsDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/FairValueMeasurementsScheduleofNonrecurringFairValueMeasurementsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongLivedAssetsHeldForSaleLineItems_019c1ff6-d89b-7ef9-8e68-28fde1f48b42" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongLivedAssetsHeldForSaleLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfLongLivedAssetsHeldForSaleTable_019c1ff6-d89b-71ba-b73e-b2231ca0cd17" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfLongLivedAssetsHeldForSaleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LongLivedAssetsHeldForSaleLineItems_019c1ff6-d89b-7ef9-8e68-28fde1f48b42" xlink:to="loc_us-gaap_ScheduleOfLongLivedAssetsHeldForSaleTable_019c1ff6-d89b-71ba-b73e-b2231ca0cd17" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019c1ff6-d89b-7ff5-b1c9-553b8c99208b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfLongLivedAssetsHeldForSaleTable_019c1ff6-d89b-71ba-b73e-b2231ca0cd17" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019c1ff6-d89b-7ff5-b1c9-553b8c99208b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019c1ff6-d89b-7ff5-b1c9-553b8c99208b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019c1ff6-d89b-7ff5-b1c9-553b8c99208b" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019c1ff6-d89b-7ff5-b1c9-553b8c99208b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_019c1ff6-d89b-78ab-8d5d-3b113ea63f28" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_019c1ff6-d89b-7ff5-b1c9-553b8c99208b" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_019c1ff6-d89b-78ab-8d5d-3b113ea63f28" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsNonrecurringMember_019c1ff6-d89b-75a7-a405-6ae27b2a098b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsNonrecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_019c1ff6-d89b-78ab-8d5d-3b113ea63f28" xlink:to="loc_us-gaap_FairValueMeasurementsNonrecurringMember_019c1ff6-d89b-75a7-a405-6ae27b2a098b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanAxis_019c1ff6-d89b-72b5-9e06-5c0e484bdbbc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfLongLivedAssetsHeldForSaleTable_019c1ff6-d89b-71ba-b73e-b2231ca0cd17" xlink:to="loc_us-gaap_RestructuringPlanAxis_019c1ff6-d89b-72b5-9e06-5c0e484bdbbc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_019c1ff6-d89b-72b5-9e06-5c0e484bdbbc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringPlanAxis_019c1ff6-d89b-72b5-9e06-5c0e484bdbbc" xlink:to="loc_us-gaap_RestructuringPlanDomain_019c1ff6-d89b-72b5-9e06-5c0e484bdbbc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_019c1ff6-d89b-7875-9c03-10bfe9d7def1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringPlanAxis_019c1ff6-d89b-72b5-9e06-5c0e484bdbbc" xlink:to="loc_us-gaap_RestructuringPlanDomain_019c1ff6-d89b-7875-9c03-10bfe9d7def1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_ProjectExitCostsMember_019c1ff6-d89b-73a7-bef9-7b8b14ed8237" xlink:href="apd-20260331.xsd#apd_ProjectExitCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_019c1ff6-d89b-7875-9c03-10bfe9d7def1" xlink:to="loc_apd_ProjectExitCostsMember_019c1ff6-d89b-73a7-bef9-7b8b14ed8237" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfFinancialPositionLocationActivityCapitalizationAxis_019c1ff6-d89b-746c-8e0b-70017609972a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementOfFinancialPositionLocationActivityCapitalizationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfLongLivedAssetsHeldForSaleTable_019c1ff6-d89b-71ba-b73e-b2231ca0cd17" xlink:to="loc_us-gaap_StatementOfFinancialPositionLocationActivityCapitalizationAxis_019c1ff6-d89b-746c-8e0b-70017609972a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfFinancialPositionLocationActivityCapitalizationDomain_019c1ff6-d89b-746c-8e0b-70017609972a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementOfFinancialPositionLocationActivityCapitalizationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementOfFinancialPositionLocationActivityCapitalizationAxis_019c1ff6-d89b-746c-8e0b-70017609972a" xlink:to="loc_us-gaap_StatementOfFinancialPositionLocationActivityCapitalizationDomain_019c1ff6-d89b-746c-8e0b-70017609972a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfFinancialPositionLocationActivityCapitalizationDomain_019c1ff6-d89b-7ba2-b8d3-cfae9d5725af" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementOfFinancialPositionLocationActivityCapitalizationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementOfFinancialPositionLocationActivityCapitalizationAxis_019c1ff6-d89b-746c-8e0b-70017609972a" xlink:to="loc_us-gaap_StatementOfFinancialPositionLocationActivityCapitalizationDomain_019c1ff6-d89b-7ba2-b8d3-cfae9d5725af" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_DisposalGroupIncludingDiscontinuedOperationAssetsCurrentMember_019c1ff6-d89b-73d3-b7b5-e416ccbb2da4" xlink:href="apd-20260331.xsd#apd_DisposalGroupIncludingDiscontinuedOperationAssetsCurrentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementOfFinancialPositionLocationActivityCapitalizationDomain_019c1ff6-d89b-7ba2-b8d3-cfae9d5725af" xlink:to="loc_apd_DisposalGroupIncludingDiscontinuedOperationAssetsCurrentMember_019c1ff6-d89b-73d3-b7b5-e416ccbb2da4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentMember_019c1ff6-d89b-777a-93fe-5cfaae23ddc7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementOfFinancialPositionLocationActivityCapitalizationDomain_019c1ff6-d89b-7ba2-b8d3-cfae9d5725af" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentMember_019c1ff6-d89b-777a-93fe-5cfaae23ddc7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019c1ff6-d89b-7fea-b821-698cfdf5846d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfLongLivedAssetsHeldForSaleTable_019c1ff6-d89b-71ba-b73e-b2231ca0cd17" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019c1ff6-d89b-7fea-b821-698cfdf5846d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019c1ff6-d89b-7fea-b821-698cfdf5846d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019c1ff6-d89b-7fea-b821-698cfdf5846d" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019c1ff6-d89b-7fea-b821-698cfdf5846d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019c1ff6-d89b-749c-8d2a-0cad0bab3f8d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019c1ff6-d89b-7fea-b821-698cfdf5846d" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019c1ff6-d89b-749c-8d2a-0cad0bab3f8d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019c1ff6-d89b-7fee-8aca-0d6cb73914d2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019c1ff6-d89b-749c-8d2a-0cad0bab3f8d" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019c1ff6-d89b-7fee-8aca-0d6cb73914d2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfLongLivedAssetsToBeDisposedOf_019c1ff6-d89b-764a-847e-4f43d17e6b58" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ImpairmentOfLongLivedAssetsToBeDisposedOf"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongLivedAssetsHeldForSaleLineItems_019c1ff6-d89b-7ef9-8e68-28fde1f48b42" xlink:to="loc_us-gaap_ImpairmentOfLongLivedAssetsToBeDisposedOf_019c1ff6-d89b-764a-847e-4f43d17e6b58" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationPropertyPlantAndEquipmentCurrent_019c1ff6-d89b-7175-8459-941c295d0978" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationPropertyPlantAndEquipmentCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongLivedAssetsHeldForSaleLineItems_019c1ff6-d89b-7ef9-8e68-28fde1f48b42" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationPropertyPlantAndEquipmentCurrent_019c1ff6-d89b-7175-8459-941c295d0978" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019c1ff6-d89b-7a1d-934d-098894a58a3d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongLivedAssetsHeldForSaleLineItems_019c1ff6-d89b-7ef9-8e68-28fde1f48b42" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019c1ff6-d89b-7a1d-934d-098894a58a3d" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/DebtUSCommittedCreditFacilitiesDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#DebtUSCommittedCreditFacilitiesDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/DebtUSCommittedCreditFacilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019c1ff6-d958-705d-adcc-f0db26dbc871" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019c1ff6-d958-7814-a318-4fa02afe1076" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019c1ff6-d958-705d-adcc-f0db26dbc871" xlink:to="loc_us-gaap_DebtInstrumentTable_019c1ff6-d958-7814-a318-4fa02afe1076" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019c1ff6-d958-7cbc-89d4-79bbb85f8af7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019c1ff6-d958-7814-a318-4fa02afe1076" xlink:to="loc_us-gaap_CreditFacilityAxis_019c1ff6-d958-7cbc-89d4-79bbb85f8af7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019c1ff6-d958-7cbc-89d4-79bbb85f8af7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019c1ff6-d958-7cbc-89d4-79bbb85f8af7" xlink:to="loc_us-gaap_CreditFacilityDomain_019c1ff6-d958-7cbc-89d4-79bbb85f8af7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019c1ff6-d958-7a49-b555-3669b1e192a1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019c1ff6-d958-7cbc-89d4-79bbb85f8af7" xlink:to="loc_us-gaap_CreditFacilityDomain_019c1ff6-d958-7a49-b555-3669b1e192a1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_019c1ff6-d958-7293-91d3-8e3ce848e4ee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019c1ff6-d958-7a49-b555-3669b1e192a1" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_019c1ff6-d958-7293-91d3-8e3ce848e4ee" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019c1ff6-d958-75c8-bf46-6199d7cbe0f3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019c1ff6-d958-7814-a318-4fa02afe1076" xlink:to="loc_us-gaap_DebtInstrumentAxis_019c1ff6-d958-75c8-bf46-6199d7cbe0f3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019c1ff6-d958-75c8-bf46-6199d7cbe0f3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019c1ff6-d958-75c8-bf46-6199d7cbe0f3" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019c1ff6-d958-75c8-bf46-6199d7cbe0f3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019c1ff6-d958-742a-b043-df3d1cb4e4bf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019c1ff6-d958-75c8-bf46-6199d7cbe0f3" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019c1ff6-d958-742a-b043-df3d1cb4e4bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_A364DayCreditAgreementMember_019c1ff6-d958-701f-b966-d518e79d555a" xlink:href="apd-20260331.xsd#apd_A364DayCreditAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019c1ff6-d958-742a-b043-df3d1cb4e4bf" xlink:to="loc_apd_A364DayCreditAgreementMember_019c1ff6-d958-701f-b966-d518e79d555a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_A2024CreditAgreementMember_019c1ff6-d958-7eab-8ee6-a85a71dacd07" xlink:href="apd-20260331.xsd#apd_A2024CreditAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019c1ff6-d958-742a-b043-df3d1cb4e4bf" xlink:to="loc_apd_A2024CreditAgreementMember_019c1ff6-d958-7eab-8ee6-a85a71dacd07" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeAxis_019c1ff6-d958-7a00-8807-e3a2cd253eaf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShortTermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019c1ff6-d958-7814-a318-4fa02afe1076" xlink:to="loc_us-gaap_ShortTermDebtTypeAxis_019c1ff6-d958-7a00-8807-e3a2cd253eaf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeDomain_019c1ff6-d958-7a00-8807-e3a2cd253eaf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShortTermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ShortTermDebtTypeAxis_019c1ff6-d958-7a00-8807-e3a2cd253eaf" xlink:to="loc_us-gaap_ShortTermDebtTypeDomain_019c1ff6-d958-7a00-8807-e3a2cd253eaf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeDomain_019c1ff6-d958-7d60-b424-a7c2ed4e496e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShortTermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ShortTermDebtTypeAxis_019c1ff6-d958-7a00-8807-e3a2cd253eaf" xlink:to="loc_us-gaap_ShortTermDebtTypeDomain_019c1ff6-d958-7d60-b424-a7c2ed4e496e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_019c1ff6-d958-7713-befc-68738dee57ad" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtTypeDomain_019c1ff6-d958-7d60-b424-a7c2ed4e496e" xlink:to="loc_us-gaap_LineOfCreditMember_019c1ff6-d958-7713-befc-68738dee57ad" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019c1ff6-d958-7c45-91f0-ae07e028848c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019c1ff6-d958-7814-a318-4fa02afe1076" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019c1ff6-d958-7c45-91f0-ae07e028848c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019c1ff6-d958-7c45-91f0-ae07e028848c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019c1ff6-d958-7c45-91f0-ae07e028848c" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019c1ff6-d958-7c45-91f0-ae07e028848c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019c1ff6-d958-7e20-87bb-4fd65c255e04" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019c1ff6-d958-7c45-91f0-ae07e028848c" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019c1ff6-d958-7e20-87bb-4fd65c255e04" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_019c1ff6-d958-7db7-abc4-47c2708efaa9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019c1ff6-d958-7e20-87bb-4fd65c255e04" xlink:to="loc_us-gaap_LineOfCreditMember_019c1ff6-d958-7db7-abc4-47c2708efaa9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTerm_019c1ff6-d958-719f-a9cb-678b1f3e9ca4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019c1ff6-d958-705d-adcc-f0db26dbc871" xlink:to="loc_us-gaap_DebtInstrumentTerm_019c1ff6-d958-719f-a9cb-678b1f3e9ca4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019c1ff6-d958-7da2-b6ed-a5a77a2f94f8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019c1ff6-d958-705d-adcc-f0db26dbc871" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019c1ff6-d958-7da2-b6ed-a5a77a2f94f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_019d96d0-00f6-7a61-877b-8c3752f12b32" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019c1ff6-d958-705d-adcc-f0db26dbc871" xlink:to="loc_us-gaap_LineOfCredit_019d96d0-00f6-7a61-877b-8c3752f12b32" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/DebtRepaymentsDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#DebtRepaymentsDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/DebtRepaymentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019d8c3c-a767-7fde-8e4f-5b7ea1d44489" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019d8c3c-a767-7e15-bf24-ab775fb420cf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d8c3c-a767-7fde-8e4f-5b7ea1d44489" xlink:to="loc_us-gaap_DebtInstrumentTable_019d8c3c-a767-7e15-bf24-ab775fb420cf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019d8c3c-a767-77c3-8b58-d764e9a45a84" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019d8c3c-a767-7e15-bf24-ab775fb420cf" xlink:to="loc_us-gaap_DebtInstrumentAxis_019d8c3c-a767-77c3-8b58-d764e9a45a84" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019d8c3c-a767-77c3-8b58-d764e9a45a84_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019d8c3c-a767-77c3-8b58-d764e9a45a84" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019d8c3c-a767-77c3-8b58-d764e9a45a84_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019d8c3c-a767-771e-8882-1a35c6ca72a8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019d8c3c-a767-77c3-8b58-d764e9a45a84" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019d8c3c-a767-771e-8882-1a35c6ca72a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_SeniorNoteOnePointFivePercentMember_019d8c3c-a767-7f16-881f-2415ae03fbde" xlink:href="apd-20260331.xsd#apd_SeniorNoteOnePointFivePercentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019d8c3c-a767-771e-8882-1a35c6ca72a8" xlink:to="loc_apd_SeniorNoteOnePointFivePercentMember_019d8c3c-a767-7f16-881f-2415ae03fbde" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019d8c3c-a767-76b1-9e92-95944afcd0ea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019d8c3c-a767-7e15-bf24-ab775fb420cf" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019d8c3c-a767-76b1-9e92-95944afcd0ea" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019d8c3c-a767-76b1-9e92-95944afcd0ea_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019d8c3c-a767-76b1-9e92-95944afcd0ea" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019d8c3c-a767-76b1-9e92-95944afcd0ea_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019d8c3c-a767-77d6-84da-d1b16dd35cb7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019d8c3c-a767-76b1-9e92-95944afcd0ea" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019d8c3c-a767-77d6-84da-d1b16dd35cb7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_019d8c3c-a767-7dfa-b7c9-8a0be34a7dcb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019d8c3c-a767-77d6-84da-d1b16dd35cb7" xlink:to="loc_us-gaap_SeniorNotesMember_019d8c3c-a767-7dfa-b7c9-8a0be34a7dcb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLongTermDebt_019d8c3c-a767-7000-872d-d24baf8f3c18" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RepaymentsOfLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d8c3c-a767-7fde-8e4f-5b7ea1d44489" xlink:to="loc_us-gaap_RepaymentsOfLongTermDebt_019d8c3c-a767-7000-872d-d24baf8f3c18" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019d8c3c-a767-74d4-9d2a-1cc0d2c81d2c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019d8c3c-a767-7fde-8e4f-5b7ea1d44489" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019d8c3c-a767-74d4-9d2a-1cc0d2c81d2c" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/RetirementBenefitsScheduleofNetPeriodicBenefitCostDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#RetirementBenefitsScheduleofNetPeriodicBenefitCostDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/RetirementBenefitsScheduleofNetPeriodicBenefitCostDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_019c1ff6-d89b-7cf0-ac8a-927452799fd6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_019c1ff6-d89b-7aac-8422-ffcd61f37eb8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_019c1ff6-d89b-7cf0-ac8a-927452799fd6" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_019c1ff6-d89b-7aac-8422-ffcd61f37eb8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanSponsorLocationAxis_019c1ff6-d89b-7f4f-ae5f-0188ab8af5c4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanSponsorLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_019c1ff6-d89b-7aac-8422-ffcd61f37eb8" xlink:to="loc_us-gaap_RetirementPlanSponsorLocationAxis_019c1ff6-d89b-7f4f-ae5f-0188ab8af5c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanSponsorLocationDomain_019c1ff6-d89b-7f4f-ae5f-0188ab8af5c4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanSponsorLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanSponsorLocationAxis_019c1ff6-d89b-7f4f-ae5f-0188ab8af5c4" xlink:to="loc_us-gaap_RetirementPlanSponsorLocationDomain_019c1ff6-d89b-7f4f-ae5f-0188ab8af5c4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanSponsorLocationDomain_019c1ff6-d89b-7457-805c-e82941670ff1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanSponsorLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanSponsorLocationAxis_019c1ff6-d89b-7f4f-ae5f-0188ab8af5c4" xlink:to="loc_us-gaap_RetirementPlanSponsorLocationDomain_019c1ff6-d89b-7457-805c-e82941670ff1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DomesticPlanMember_019c1ff6-d89b-72e3-896d-b203ddca806a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DomesticPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanSponsorLocationDomain_019c1ff6-d89b-7457-805c-e82941670ff1" xlink:to="loc_us-gaap_DomesticPlanMember_019c1ff6-d89b-72e3-896d-b203ddca806a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_019c1ff6-d89b-74d9-acc5-98df8f1efb63" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DomesticPlanMember_019c1ff6-d89b-72e3-896d-b203ddca806a" xlink:to="loc_country_US_019c1ff6-d89b-74d9-acc5-98df8f1efb63" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignPlanMember_019c1ff6-d89b-7609-99be-d2d396c73f51" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForeignPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanSponsorLocationDomain_019c1ff6-d89b-7457-805c-e82941670ff1" xlink:to="loc_us-gaap_ForeignPlanMember_019c1ff6-d89b-7609-99be-d2d396c73f51" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_019c1ff6-d89b-7773-a7fe-0c8487f2a8db" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_019c1ff6-d89b-7aac-8422-ffcd61f37eb8" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_019c1ff6-d89b-7773-a7fe-0c8487f2a8db" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_019c1ff6-d89b-7773-a7fe-0c8487f2a8db_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_019c1ff6-d89b-7773-a7fe-0c8487f2a8db" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_019c1ff6-d89b-7773-a7fe-0c8487f2a8db_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_019c1ff6-d89b-76a6-9c3d-a1fd3163044a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_019c1ff6-d89b-7773-a7fe-0c8487f2a8db" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_019c1ff6-d89b-76a6-9c3d-a1fd3163044a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_019c1ff6-d89b-73a5-81be-ae9edee8573f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_019c1ff6-d89b-76a6-9c3d-a1fd3163044a" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_019c1ff6-d89b-73a5-81be-ae9edee8573f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanServiceCost_019c1ff6-d89b-7769-9f97-d8561c035b41" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanServiceCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_019c1ff6-d89b-7cf0-ac8a-927452799fd6" xlink:to="loc_us-gaap_DefinedBenefitPlanServiceCost_019c1ff6-d89b-7769-9f97-d8561c035b41" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanInterestCost_019c1ff6-d89b-7ff7-8ba6-7cd77a9a907f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanInterestCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_019c1ff6-d89b-7cf0-ac8a-927452799fd6" xlink:to="loc_us-gaap_DefinedBenefitPlanInterestCost_019c1ff6-d89b-7ff7-8ba6-7cd77a9a907f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets_019c1ff6-d89b-7ebe-98ca-1411959d6a81" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_019c1ff6-d89b-7cf0-ac8a-927452799fd6" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets_019c1ff6-d89b-7ebe-98ca-1411959d6a81" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit_019c1ff6-d89b-766e-826e-61f6176dafa7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_019c1ff6-d89b-7cf0-ac8a-927452799fd6" xlink:to="loc_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit_019c1ff6-d89b-766e-826e-61f6176dafa7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses_019c1ff6-d89b-76cf-b93e-7c588c345abd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_019c1ff6-d89b-7cf0-ac8a-927452799fd6" xlink:to="loc_us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses_019c1ff6-d89b-76cf-b93e-7c588c345abd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1_019db717-7dc5-7caa-b155-8ccdb1902200" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_019c1ff6-d89b-7cf0-ac8a-927452799fd6" xlink:to="loc_us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1_019db717-7dc5-7caa-b155-8ccdb1902200" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanOtherCosts_019c1ff6-d89b-748e-8bef-5df643e018c0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanOtherCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_019c1ff6-d89b-7cf0-ac8a-927452799fd6" xlink:to="loc_us-gaap_DefinedBenefitPlanOtherCosts_019c1ff6-d89b-748e-8bef-5df643e018c0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_019c1ff6-d89b-7234-b861-18efec84cf29" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_019c1ff6-d89b-7cf0-ac8a-927452799fd6" xlink:to="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_019c1ff6-d89b-7234-b861-18efec84cf29" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostCreditExcludingServiceCostStatementOfIncomeOrComprehensiveIncomeExtensibleList_019c1ff6-d89b-7c44-b460-fa080229e317" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostCreditExcludingServiceCostStatementOfIncomeOrComprehensiveIncomeExtensibleList"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_019c1ff6-d89b-7234-b861-18efec84cf29" xlink:to="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostCreditExcludingServiceCostStatementOfIncomeOrComprehensiveIncomeExtensibleList_019c1ff6-d89b-7c44-b460-fa080229e317" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/RetirementBenefitsNarrativeDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#RetirementBenefitsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/RetirementBenefitsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_019c1ff6-d89b-7404-991e-0a63e0a2f605" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_019c1ff6-d89b-7bb9-b88a-9b31b601ef74" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_019c1ff6-d89b-7404-991e-0a63e0a2f605" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_019c1ff6-d89b-7bb9-b88a-9b31b601ef74" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_019c1ff6-d89b-72bc-a24d-dc91a37a16fb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_019c1ff6-d89b-7bb9-b88a-9b31b601ef74" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_019c1ff6-d89b-72bc-a24d-dc91a37a16fb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_019c1ff6-d89b-72bc-a24d-dc91a37a16fb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_019c1ff6-d89b-72bc-a24d-dc91a37a16fb" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_019c1ff6-d89b-72bc-a24d-dc91a37a16fb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_019c1ff6-d89b-7df8-9645-03fcfc113997" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_019c1ff6-d89b-72bc-a24d-dc91a37a16fb" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_019c1ff6-d89b-7df8-9645-03fcfc113997" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_019c1ff6-d89b-76ee-9744-c22eff78ce82" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_019c1ff6-d89b-7df8-9645-03fcfc113997" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_019c1ff6-d89b-76ee-9744-c22eff78ce82" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_019c1ff6-d89b-79b2-9907-e6ae8dbf41e2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_019c1ff6-d89b-7df8-9645-03fcfc113997" xlink:to="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_019c1ff6-d89b-79b2-9907-e6ae8dbf41e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019c1ff6-d89b-720c-bb90-e88fbe8a6917" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_019c1ff6-d89b-7bb9-b88a-9b31b601ef74" xlink:to="loc_srt_RangeAxis_019c1ff6-d89b-720c-bb90-e88fbe8a6917" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019c1ff6-d89b-720c-bb90-e88fbe8a6917_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019c1ff6-d89b-720c-bb90-e88fbe8a6917" xlink:to="loc_srt_RangeMember_019c1ff6-d89b-720c-bb90-e88fbe8a6917_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019c1ff6-d89b-7f4b-89d6-60d06982e1dd" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019c1ff6-d89b-720c-bb90-e88fbe8a6917" xlink:to="loc_srt_RangeMember_019c1ff6-d89b-7f4b-89d6-60d06982e1dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019c1ff6-d89b-7ed6-b9e1-38d1c10ca73f" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019c1ff6-d89b-7f4b-89d6-60d06982e1dd" xlink:to="loc_srt_MinimumMember_019c1ff6-d89b-7ed6-b9e1-38d1c10ca73f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019c1ff6-d89b-7c32-9aa5-324aff4d0a73" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019c1ff6-d89b-7f4b-89d6-60d06982e1dd" xlink:to="loc_srt_MaximumMember_019c1ff6-d89b-7c32-9aa5-324aff4d0a73" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanSponsorLocationAxis_019c1ff6-d89b-7452-a46c-9da772fa96bb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanSponsorLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_019c1ff6-d89b-7bb9-b88a-9b31b601ef74" xlink:to="loc_us-gaap_RetirementPlanSponsorLocationAxis_019c1ff6-d89b-7452-a46c-9da772fa96bb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanSponsorLocationDomain_019c1ff6-d89b-7452-a46c-9da772fa96bb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanSponsorLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanSponsorLocationAxis_019c1ff6-d89b-7452-a46c-9da772fa96bb" xlink:to="loc_us-gaap_RetirementPlanSponsorLocationDomain_019c1ff6-d89b-7452-a46c-9da772fa96bb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanSponsorLocationDomain_019c1ff6-d89b-7fe5-ac18-ae3acc54cb0e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanSponsorLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanSponsorLocationAxis_019c1ff6-d89b-7452-a46c-9da772fa96bb" xlink:to="loc_us-gaap_RetirementPlanSponsorLocationDomain_019c1ff6-d89b-7fe5-ac18-ae3acc54cb0e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignPlanMember_019c1ff6-d89b-7d57-a443-f449dcd3a22f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForeignPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanSponsorLocationDomain_019c1ff6-d89b-7fe5-ac18-ae3acc54cb0e" xlink:to="loc_us-gaap_ForeignPlanMember_019c1ff6-d89b-7d57-a443-f449dcd3a22f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanContributionsByEmployer_019c1ff6-d89b-74d0-b78a-f3b29bbf7530" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanContributionsByEmployer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_019c1ff6-d89b-7404-991e-0a63e0a2f605" xlink:to="loc_us-gaap_DefinedBenefitPlanContributionsByEmployer_019c1ff6-d89b-74d0-b78a-f3b29bbf7530" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsCurrentFiscalYear_019c1ff6-d89b-7993-a06c-2b376eafa767" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsCurrentFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_019c1ff6-d89b-7404-991e-0a63e0a2f605" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsCurrentFiscalYear_019c1ff6-d89b-7993-a06c-2b376eafa767" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax_019c1ff6-d89b-77f9-a2df-29532414daf9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_019c1ff6-d89b-7404-991e-0a63e0a2f605" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax_019c1ff6-d89b-77f9-a2df-29532414daf9" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/CommitmentsandContingenciesLitigationandEnvironmentalNarrativeDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#CommitmentsandContingenciesLitigationandEnvironmentalNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/CommitmentsandContingenciesLitigationandEnvironmentalNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_019c1ff6-d89b-74fe-bff4-9268d058f79b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_019c1ff6-d89b-7b50-ae6e-c5bee8d662dd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_019c1ff6-d89b-74fe-bff4-9268d058f79b" xlink:to="loc_us-gaap_LossContingenciesTable_019c1ff6-d89b-7b50-ae6e-c5bee8d662dd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_019c1ff6-d89b-7b52-afdb-c04e1f49ce82" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingenciesByNatureOfContingencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019c1ff6-d89b-7b50-ae6e-c5bee8d662dd" xlink:to="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_019c1ff6-d89b-7b52-afdb-c04e1f49ce82" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_019c1ff6-d89b-7b52-afdb-c04e1f49ce82_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_019c1ff6-d89b-7b52-afdb-c04e1f49ce82" xlink:to="loc_us-gaap_LossContingencyNatureDomain_019c1ff6-d89b-7b52-afdb-c04e1f49ce82_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_019c1ff6-d89b-72ea-b337-d0fc3dfe0297" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_019c1ff6-d89b-7b52-afdb-c04e1f49ce82" xlink:to="loc_us-gaap_LossContingencyNatureDomain_019c1ff6-d89b-72ea-b337-d0fc3dfe0297" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EnvironmentalIssueMember_019c1ff6-d89b-7095-9dce-cb64d649b9e9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EnvironmentalIssueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingencyNatureDomain_019c1ff6-d89b-72ea-b337-d0fc3dfe0297" xlink:to="loc_us-gaap_EnvironmentalIssueMember_019c1ff6-d89b-7095-9dce-cb64d649b9e9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainContingenciesByNatureAxis_019c1ff6-d89b-77cb-a148-d104ce551dda" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GainContingenciesByNatureAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019c1ff6-d89b-7b50-ae6e-c5bee8d662dd" xlink:to="loc_us-gaap_GainContingenciesByNatureAxis_019c1ff6-d89b-77cb-a148-d104ce551dda" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainContingencyNatureDomain_019c1ff6-d89b-77cb-a148-d104ce551dda_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GainContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_GainContingenciesByNatureAxis_019c1ff6-d89b-77cb-a148-d104ce551dda" xlink:to="loc_us-gaap_GainContingencyNatureDomain_019c1ff6-d89b-77cb-a148-d104ce551dda_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainContingencyNatureDomain_019c1ff6-d89b-7738-b760-c8d21b2c9f08" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GainContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_GainContingenciesByNatureAxis_019c1ff6-d89b-77cb-a148-d104ce551dda" xlink:to="loc_us-gaap_GainContingencyNatureDomain_019c1ff6-d89b-7738-b760-c8d21b2c9f08" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019c1ff6-d89b-7e8a-b30c-12ca97fc3534" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019c1ff6-d89b-7b50-ae6e-c5bee8d662dd" xlink:to="loc_srt_RangeAxis_019c1ff6-d89b-7e8a-b30c-12ca97fc3534" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019c1ff6-d89b-7e8a-b30c-12ca97fc3534_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019c1ff6-d89b-7e8a-b30c-12ca97fc3534" xlink:to="loc_srt_RangeMember_019c1ff6-d89b-7e8a-b30c-12ca97fc3534_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019c1ff6-d89b-7a82-837e-4ed37907ef56" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019c1ff6-d89b-7e8a-b30c-12ca97fc3534" xlink:to="loc_srt_RangeMember_019c1ff6-d89b-7a82-837e-4ed37907ef56" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019c1ff6-d89b-7896-a876-5921420056aa" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019c1ff6-d89b-7a82-837e-4ed37907ef56" xlink:to="loc_srt_MinimumMember_019c1ff6-d89b-7896-a876-5921420056aa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019c1ff6-d89b-7c52-ae3e-680e2fb17961" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019c1ff6-d89b-7a82-837e-4ed37907ef56" xlink:to="loc_srt_MaximumMember_019c1ff6-d89b-7c52-ae3e-680e2fb17961" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_SitesOnWhichFinalSettlementHasNotBeenReached_019c1ff6-d89b-7e94-9dbe-5cab80c448d0" xlink:href="apd-20260331.xsd#apd_SitesOnWhichFinalSettlementHasNotBeenReached"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019c1ff6-d89b-74fe-bff4-9268d058f79b" xlink:to="loc_apd_SitesOnWhichFinalSettlementHasNotBeenReached_019c1ff6-d89b-7e94-9dbe-5cab80c448d0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccrualForEnvironmentalLossContingencies_019c1ff6-d89b-75c8-91ee-2d0178864074" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccrualForEnvironmentalLossContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019c1ff6-d89b-74fe-bff4-9268d058f79b" xlink:to="loc_us-gaap_AccrualForEnvironmentalLossContingencies_019c1ff6-d89b-75c8-91ee-2d0178864074" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SiteContingencyDisbursementPeriodEstimateAccrued_019c1ff6-d89b-7542-af4f-7e37fe67056f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SiteContingencyDisbursementPeriodEstimateAccrued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019c1ff6-d89b-74fe-bff4-9268d058f79b" xlink:to="loc_us-gaap_SiteContingencyDisbursementPeriodEstimateAccrued_019c1ff6-d89b-7542-af4f-7e37fe67056f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyEstimateOfPossibleLoss_019c1ff6-d89b-794d-9da6-f7a3507a5bbc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingencyEstimateOfPossibleLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019c1ff6-d89b-74fe-bff4-9268d058f79b" xlink:to="loc_us-gaap_LossContingencyEstimateOfPossibleLoss_019c1ff6-d89b-794d-9da6-f7a3507a5bbc" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/CommitmentsandContingenciesPacePiedmontandPasadenaNarrativeDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#CommitmentsandContingenciesPacePiedmontandPasadenaNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/CommitmentsandContingenciesPacePiedmontandPasadenaNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_019c1ff6-d89b-7296-a3e8-cd6842703e3b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_019c1ff6-d89b-726a-b1e9-6426ad78fd6b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_019c1ff6-d89b-7296-a3e8-cd6842703e3b" xlink:to="loc_us-gaap_LossContingenciesTable_019c1ff6-d89b-726a-b1e9-6426ad78fd6b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EnvironmentalRemediationSiteAxis_019c1ff6-d89b-7633-bdc7-f63765920455" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EnvironmentalRemediationSiteAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019c1ff6-d89b-726a-b1e9-6426ad78fd6b" xlink:to="loc_us-gaap_EnvironmentalRemediationSiteAxis_019c1ff6-d89b-7633-bdc7-f63765920455" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EnvironmentalRemediationSiteDomain_019c1ff6-d89b-7633-bdc7-f63765920455_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EnvironmentalRemediationSiteDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_EnvironmentalRemediationSiteAxis_019c1ff6-d89b-7633-bdc7-f63765920455" xlink:to="loc_us-gaap_EnvironmentalRemediationSiteDomain_019c1ff6-d89b-7633-bdc7-f63765920455_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EnvironmentalRemediationSiteDomain_019c1ff6-d89b-7267-9697-c41284f18738" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EnvironmentalRemediationSiteDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_EnvironmentalRemediationSiteAxis_019c1ff6-d89b-7633-bdc7-f63765920455" xlink:to="loc_us-gaap_EnvironmentalRemediationSiteDomain_019c1ff6-d89b-7267-9697-c41284f18738" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_PaceFloridaMember_019c1ff6-d89b-70ae-8ea5-ab40f6e6476a" xlink:href="apd-20260331.xsd#apd_PaceFloridaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EnvironmentalRemediationSiteDomain_019c1ff6-d89b-7267-9697-c41284f18738" xlink:to="loc_apd_PaceFloridaMember_019c1ff6-d89b-70ae-8ea5-ab40f6e6476a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_PiedmontSouthCarolinaMember_019c1ff6-d89b-7ccd-b038-374f95e2a8dc" xlink:href="apd-20260331.xsd#apd_PiedmontSouthCarolinaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EnvironmentalRemediationSiteDomain_019c1ff6-d89b-7267-9697-c41284f18738" xlink:to="loc_apd_PiedmontSouthCarolinaMember_019c1ff6-d89b-7ccd-b038-374f95e2a8dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_PasadenaTexasMemberMember_019c1ff6-d89b-7699-8c5b-34dbeba6a0dc" xlink:href="apd-20260331.xsd#apd_PasadenaTexasMemberMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EnvironmentalRemediationSiteDomain_019c1ff6-d89b-7267-9697-c41284f18738" xlink:to="loc_apd_PasadenaTexasMemberMember_019c1ff6-d89b-7699-8c5b-34dbeba6a0dc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_019c1ff6-d89b-71eb-ba90-3959d6a72ae1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementOperatingActivitiesSegmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019c1ff6-d89b-726a-b1e9-6426ad78fd6b" xlink:to="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_019c1ff6-d89b-71eb-ba90-3959d6a72ae1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentOperatingActivitiesDomain_019c1ff6-d89b-71eb-ba90-3959d6a72ae1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentOperatingActivitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_019c1ff6-d89b-71eb-ba90-3959d6a72ae1" xlink:to="loc_us-gaap_SegmentOperatingActivitiesDomain_019c1ff6-d89b-71eb-ba90-3959d6a72ae1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentOperatingActivitiesDomain_019c1ff6-d89b-7455-ab79-6a9dd03c2ce2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentOperatingActivitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_019c1ff6-d89b-71eb-ba90-3959d6a72ae1" xlink:to="loc_us-gaap_SegmentOperatingActivitiesDomain_019c1ff6-d89b-7455-ab79-6a9dd03c2ce2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDiscontinuedOperationsMember_019c1ff6-d89b-78fa-9a08-ff80442d467d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDiscontinuedOperationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentOperatingActivitiesDomain_019c1ff6-d89b-7455-ab79-6a9dd03c2ce2" xlink:to="loc_us-gaap_SegmentDiscontinuedOperationsMember_019c1ff6-d89b-78fa-9a08-ff80442d467d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_019c1ff6-d89b-7c0b-a474-853e8f56ec8c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingenciesByNatureOfContingencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019c1ff6-d89b-726a-b1e9-6426ad78fd6b" xlink:to="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_019c1ff6-d89b-7c0b-a474-853e8f56ec8c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_019c1ff6-d89b-7c0b-a474-853e8f56ec8c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_019c1ff6-d89b-7c0b-a474-853e8f56ec8c" xlink:to="loc_us-gaap_LossContingencyNatureDomain_019c1ff6-d89b-7c0b-a474-853e8f56ec8c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_019c1ff6-d89b-72eb-a4d4-faef44bc6034" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_019c1ff6-d89b-7c0b-a474-853e8f56ec8c" xlink:to="loc_us-gaap_LossContingencyNatureDomain_019c1ff6-d89b-72eb-a4d4-faef44bc6034" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EnvironmentalIssueMember_019c1ff6-d89b-74f3-bca3-de6b8493f156" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EnvironmentalIssueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingencyNatureDomain_019c1ff6-d89b-72eb-a4d4-faef44bc6034" xlink:to="loc_us-gaap_EnvironmentalIssueMember_019c1ff6-d89b-74f3-bca3-de6b8493f156" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccrualForEnvironmentalLossContingencies_019c1ff6-d89b-7175-b737-ad2de5493d6c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccrualForEnvironmentalLossContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019c1ff6-d89b-7296-a3e8-cd6842703e3b" xlink:to="loc_us-gaap_AccrualForEnvironmentalLossContingencies_019c1ff6-d89b-7175-b737-ad2de5493d6c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EnvironmentalRemediationExpense_019c1ff6-d89b-7be1-a8fa-29134acabea9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EnvironmentalRemediationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019c1ff6-d89b-7296-a3e8-cd6842703e3b" xlink:to="loc_us-gaap_EnvironmentalRemediationExpense_019c1ff6-d89b-7be1-a8fa-29134acabea9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_SiteContingencyCostReviewPeriod_019c1ff6-d89b-7e3d-9058-b548668a5650" xlink:href="apd-20260331.xsd#apd_SiteContingencyCostReviewPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019c1ff6-d89b-7296-a3e8-cd6842703e3b" xlink:to="loc_apd_SiteContingencyCostReviewPeriod_019c1ff6-d89b-7e3d-9058-b548668a5650" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccrualForEnvironmentalLossContingenciesIncreaseDecreaseForRevisionInEstimates_019c1ff6-d89b-7186-bcf3-8ef4f06472db" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccrualForEnvironmentalLossContingenciesIncreaseDecreaseForRevisionInEstimates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019c1ff6-d89b-7296-a3e8-cd6842703e3b" xlink:to="loc_us-gaap_AccrualForEnvironmentalLossContingenciesIncreaseDecreaseForRevisionInEstimates_019c1ff6-d89b-7186-bcf3-8ef4f06472db" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SiteContingencyDisbursementPeriodEstimateAccrued_019c1ff6-d89b-77cf-a588-42070a2e56f7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SiteContingencyDisbursementPeriodEstimateAccrued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019c1ff6-d89b-7296-a3e8-cd6842703e3b" xlink:to="loc_us-gaap_SiteContingencyDisbursementPeriodEstimateAccrued_019c1ff6-d89b-77cf-a588-42070a2e56f7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_NumberOfClosedFacilities_019c1ff6-d89b-7759-83a4-cd7c93029fe0" xlink:href="apd-20260331.xsd#apd_NumberOfClosedFacilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019c1ff6-d89b-7296-a3e8-cd6842703e3b" xlink:to="loc_apd_NumberOfClosedFacilities_019c1ff6-d89b-7759-83a4-cd7c93029fe0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EnvironmentalExitCostsAnticipatedCost_019c1ff6-d89b-7113-80dd-7033ee9c0e2a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EnvironmentalExitCostsAnticipatedCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019c1ff6-d89b-7296-a3e8-cd6842703e3b" xlink:to="loc_us-gaap_EnvironmentalExitCostsAnticipatedCost_019c1ff6-d89b-7113-80dd-7033ee9c0e2a" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/ShareBasedCompensationNarrativeDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#ShareBasedCompensationNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/ShareBasedCompensationNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c1ff6-d89b-768e-ab75-dce489576cee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019c1ff6-d89b-7392-b48b-b4ef7c974465" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c1ff6-d89b-768e-ab75-dce489576cee" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019c1ff6-d89b-7392-b48b-b4ef7c974465" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019c1ff6-d89b-7ba3-912b-1d744d4e1738" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019c1ff6-d89b-7392-b48b-b4ef7c974465" xlink:to="loc_us-gaap_PlanNameAxis_019c1ff6-d89b-7ba3-912b-1d744d4e1738" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019c1ff6-d89b-7ba3-912b-1d744d4e1738_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_019c1ff6-d89b-7ba3-912b-1d744d4e1738" xlink:to="loc_us-gaap_PlanNameDomain_019c1ff6-d89b-7ba3-912b-1d744d4e1738_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019c1ff6-d89b-7530-a03d-0ed647299634" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_019c1ff6-d89b-7ba3-912b-1d744d4e1738" xlink:to="loc_us-gaap_PlanNameDomain_019c1ff6-d89b-7530-a03d-0ed647299634" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_LongTermIncentivePlanMember_019c1ff6-d89b-7188-a592-0608a8606ef7" xlink:href="apd-20260331.xsd#apd_LongTermIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019c1ff6-d89b-7530-a03d-0ed647299634" xlink:to="loc_apd_LongTermIncentivePlanMember_019c1ff6-d89b-7188-a592-0608a8606ef7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019c1ff6-d89b-7875-92d9-c5a3dbfb2c8f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019c1ff6-d89b-7392-b48b-b4ef7c974465" xlink:to="loc_us-gaap_AwardTypeAxis_019c1ff6-d89b-7875-92d9-c5a3dbfb2c8f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c1ff6-d89b-7875-92d9-c5a3dbfb2c8f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019c1ff6-d89b-7875-92d9-c5a3dbfb2c8f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c1ff6-d89b-7875-92d9-c5a3dbfb2c8f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c1ff6-d89b-7eb4-aa6a-f6c76a164c4c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019c1ff6-d89b-7875-92d9-c5a3dbfb2c8f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c1ff6-d89b-7eb4-aa6a-f6c76a164c4c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_019c1ff6-d89b-7abf-b5ba-40a711f50d07" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c1ff6-d89b-7eb4-aa6a-f6c76a164c4c" xlink:to="loc_us-gaap_PerformanceSharesMember_019c1ff6-d89b-7abf-b5ba-40a711f50d07" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_PerformanceSharesInternalBasedMember_019c1ff6-d89b-7d79-b835-088e06118d6f" xlink:href="apd-20260331.xsd#apd_PerformanceSharesInternalBasedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PerformanceSharesMember_019c1ff6-d89b-7abf-b5ba-40a711f50d07" xlink:to="loc_apd_PerformanceSharesInternalBasedMember_019c1ff6-d89b-7d79-b835-088e06118d6f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_PerformanceSharesMarketBasedMember_019c1ff6-d89b-71f4-a589-288f1b5679ed" xlink:href="apd-20260331.xsd#apd_PerformanceSharesMarketBasedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PerformanceSharesMember_019c1ff6-d89b-7abf-b5ba-40a711f50d07" xlink:to="loc_apd_PerformanceSharesMarketBasedMember_019c1ff6-d89b-71f4-a589-288f1b5679ed" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_TimeBasedDeferredStockUnitMember_019c1ff6-d89b-7768-946a-eaa6b91eecd3" xlink:href="apd-20260331.xsd#apd_TimeBasedDeferredStockUnitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c1ff6-d89b-7eb4-aa6a-f6c76a164c4c" xlink:to="loc_apd_TimeBasedDeferredStockUnitMember_019c1ff6-d89b-7768-946a-eaa6b91eecd3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_019c1ff6-d89b-7ed7-9a71-1f01f2dacf31" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c1ff6-d89b-768e-ab75-dce489576cee" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_019c1ff6-d89b-7ed7-9a71-1f01f2dacf31" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019c1ff6-d89b-78b4-8642-74195939e0b7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c1ff6-d89b-768e-ab75-dce489576cee" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019c1ff6-d89b-78b4-8642-74195939e0b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019c1ff6-d89b-7b38-ad4d-d43a0f103dc5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c1ff6-d89b-768e-ab75-dce489576cee" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019c1ff6-d89b-7b38-ad4d-d43a0f103dc5" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/ShareBasedCompensationCompensationCostRecognizedinIncomeStatementDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#ShareBasedCompensationCompensationCostRecognizedinIncomeStatementDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/ShareBasedCompensationCompensationCostRecognizedinIncomeStatementDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019daba7-5f2d-78f6-837e-5de86a4e4b55" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019daba7-5f2d-7bd8-a01b-47fb7bd2ed2a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019daba7-5f2d-78f6-837e-5de86a4e4b55" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019daba7-5f2d-7bd8-a01b-47fb7bd2ed2a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_019daba7-5f2d-7a66-8f57-f25c5f588add" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019daba7-5f2d-7bd8-a01b-47fb7bd2ed2a" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_019daba7-5f2d-7a66-8f57-f25c5f588add" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_019daba7-5f2d-7a66-8f57-f25c5f588add_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_019daba7-5f2d-7a66-8f57-f25c5f588add" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_019daba7-5f2d-7a66-8f57-f25c5f588add_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_019daba7-5f2d-7c19-b012-fde66c52e91c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_019daba7-5f2d-7a66-8f57-f25c5f588add" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_019daba7-5f2d-7c19-b012-fde66c52e91c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_ExecutiveSeparationCostsMember_019daba8-4a9e-799d-8f52-8ceac223978f" xlink:href="apd-20260331.xsd#apd_ExecutiveSeparationCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_019daba7-5f2d-7c19-b012-fde66c52e91c" xlink:to="loc_apd_ExecutiveSeparationCostsMember_019daba8-4a9e-799d-8f52-8ceac223978f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAcceleratedCompensationCost_019daba7-5f2d-7d86-9e58-1f0231e5e6d8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAcceleratedCompensationCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019daba7-5f2d-78f6-837e-5de86a4e4b55" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAcceleratedCompensationCost_019daba7-5f2d-7d86-9e58-1f0231e5e6d8" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/ShareBasedCompensationMarketBasedDeferredStockUnitValuationAssumptionsDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#ShareBasedCompensationMarketBasedDeferredStockUnitValuationAssumptionsDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/ShareBasedCompensationMarketBasedDeferredStockUnitValuationAssumptionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c1ff6-d89b-7927-aee0-03498a8b5c87" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019c1ff6-d89b-74c8-8486-422b44921933" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c1ff6-d89b-7927-aee0-03498a8b5c87" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019c1ff6-d89b-74c8-8486-422b44921933" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019c1ff6-d89b-7702-a859-058f7666b775" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019c1ff6-d89b-74c8-8486-422b44921933" xlink:to="loc_us-gaap_AwardTypeAxis_019c1ff6-d89b-7702-a859-058f7666b775" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c1ff6-d89b-7702-a859-058f7666b775_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019c1ff6-d89b-7702-a859-058f7666b775" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c1ff6-d89b-7702-a859-058f7666b775_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c1ff6-d89b-79e8-9601-bceae07fa3ab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019c1ff6-d89b-7702-a859-058f7666b775" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c1ff6-d89b-79e8-9601-bceae07fa3ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_MarketBasedDeferredStockUnitMember_019c1ff6-d89b-71f6-b663-9c2c067a08e7" xlink:href="apd-20260331.xsd#apd_MarketBasedDeferredStockUnitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c1ff6-d89b-79e8-9601-bceae07fa3ab" xlink:to="loc_apd_MarketBasedDeferredStockUnitMember_019c1ff6-d89b-71f6-b663-9c2c067a08e7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_019c1ff6-d89b-71e7-941d-be52c6dda734" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c1ff6-d89b-7927-aee0-03498a8b5c87" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_019c1ff6-d89b-71e7-941d-be52c6dda734" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_019c1ff6-d89b-78eb-a959-2f5efb4726e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c1ff6-d89b-7927-aee0-03498a8b5c87" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_019c1ff6-d89b-78eb-a959-2f5efb4726e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_019c1ff6-d89b-720d-9257-b71e3d823a60" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019c1ff6-d89b-7927-aee0-03498a8b5c87" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_019c1ff6-d89b-720d-9257-b71e3d823a60" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/AccumulatedOtherComprehensiveLossRollforwardDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#AccumulatedOtherComprehensiveLossRollforwardDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/AccumulatedOtherComprehensiveLossRollforwardDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019c1ff6-d89b-787a-a509-dc5851f198fd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_019c1ff6-d89b-7fc6-831e-ee9ff6436256" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019c1ff6-d89b-787a-a509-dc5851f198fd" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_019c1ff6-d89b-7fc6-831e-ee9ff6436256" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019c1ff6-d89b-7a20-82c5-9d49e490b6e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_019c1ff6-d89b-7fc6-831e-ee9ff6436256" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019c1ff6-d89b-7a20-82c5-9d49e490b6e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019c1ff6-d89b-7a20-82c5-9d49e490b6e1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019c1ff6-d89b-7a20-82c5-9d49e490b6e1" xlink:to="loc_us-gaap_EquityComponentDomain_019c1ff6-d89b-7a20-82c5-9d49e490b6e1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019c1ff6-d89b-7c86-8c8e-aaed1e3dae20" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019c1ff6-d89b-7a20-82c5-9d49e490b6e1" xlink:to="loc_us-gaap_EquityComponentDomain_019c1ff6-d89b-7c86-8c8e-aaed1e3dae20" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_019c1ff6-d89b-7740-8c2d-d6958ac27e02" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019c1ff6-d89b-7c86-8c8e-aaed1e3dae20" xlink:to="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_019c1ff6-d89b-7740-8c2d-d6958ac27e02" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedTranslationAdjustmentMember_019c1ff6-d89b-7238-abeb-648dc3ec3680" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedTranslationAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019c1ff6-d89b-7c86-8c8e-aaed1e3dae20" xlink:to="loc_us-gaap_AccumulatedTranslationAdjustmentMember_019c1ff6-d89b-7238-abeb-648dc3ec3680" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_019c1ff6-d89b-73e0-9ea1-87547dc26af0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019c1ff6-d89b-7c86-8c8e-aaed1e3dae20" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_019c1ff6-d89b-73e0-9ea1-87547dc26af0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019c1ff6-d89b-73b9-9d26-451d0f22e72c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019c1ff6-d89b-7c86-8c8e-aaed1e3dae20" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019c1ff6-d89b-73b9-9d26-451d0f22e72c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_019c1ff6-d89b-7a88-8597-2482a8cf5133" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019c1ff6-d89b-787a-a509-dc5851f198fd" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_019c1ff6-d89b-7a88-8597-2482a8cf5133" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019c1ff6-d89b-7a45-80cb-3aad933a5d3e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_019c1ff6-d89b-7a88-8597-2482a8cf5133" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019c1ff6-d89b-7a45-80cb-3aad933a5d3e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax_019c1ff6-d89b-73a3-b58d-762f3c289420" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_019c1ff6-d89b-7a88-8597-2482a8cf5133" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax_019c1ff6-d89b-73a3-b58d-762f3c289420" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_019c1ff6-d89b-7f7a-80b3-99b29027a426" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_019c1ff6-d89b-7a88-8597-2482a8cf5133" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_019c1ff6-d89b-7f7a-80b3-99b29027a426" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019c1ff6-d89b-784d-8901-343a3028236b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_019c1ff6-d89b-7a88-8597-2482a8cf5133" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_019c1ff6-d89b-784d-8901-343a3028236b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest_019c1ff6-d89b-767c-a80d-71a3cc47fd87" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_019c1ff6-d89b-7a88-8597-2482a8cf5133" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest_019c1ff6-d89b-767c-a80d-71a3cc47fd87" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019c1ff6-d89b-7c62-901d-70649d99ac89" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/AccumulatedOtherComprehensiveLossReclassificationDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#AccumulatedOtherComprehensiveLossReclassificationDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/AccumulatedOtherComprehensiveLossReclassificationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_019c1ff6-d89b-7dc1-8895-6c3d8e1c4acb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_019c1ff6-d89b-7770-a5d7-8153a6a4e137" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_019c1ff6-d89b-7dc1-8895-6c3d8e1c4acb" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_019c1ff6-d89b-7770-a5d7-8153a6a4e137" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019c1ff6-d89b-7605-bc61-edb97c6e43a7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_019c1ff6-d89b-7770-a5d7-8153a6a4e137" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019c1ff6-d89b-7605-bc61-edb97c6e43a7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019c1ff6-d89b-7605-bc61-edb97c6e43a7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019c1ff6-d89b-7605-bc61-edb97c6e43a7" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019c1ff6-d89b-7605-bc61-edb97c6e43a7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019c1ff6-d89b-7f83-8671-45e0fa78a25f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_019c1ff6-d89b-7605-bc61-edb97c6e43a7" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019c1ff6-d89b-7f83-8671-45e0fa78a25f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_019c1ff6-d89b-7581-99cd-e68a587e4d39" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_019c1ff6-d89b-7f83-8671-45e0fa78a25f" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_019c1ff6-d89b-7581-99cd-e68a587e4d39" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019c1ff6-d89b-750a-93db-eac7e4c4e0e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_019c1ff6-d89b-7770-a5d7-8153a6a4e137" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019c1ff6-d89b-750a-93db-eac7e4c4e0e1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019c1ff6-d89b-750a-93db-eac7e4c4e0e1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019c1ff6-d89b-750a-93db-eac7e4c4e0e1" xlink:to="loc_us-gaap_EquityComponentDomain_019c1ff6-d89b-750a-93db-eac7e4c4e0e1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019c1ff6-d89b-7e9b-8866-339601e9c067" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019c1ff6-d89b-750a-93db-eac7e4c4e0e1" xlink:to="loc_us-gaap_EquityComponentDomain_019c1ff6-d89b-7e9b-8866-339601e9c067" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_019c1ff6-d89b-749e-8167-2258420c4260" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019c1ff6-d89b-7e9b-8866-339601e9c067" xlink:to="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_019c1ff6-d89b-749e-8167-2258420c4260" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedTranslationAdjustmentMember_019db6d8-acff-7c91-bce9-565d4b7d87ff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedTranslationAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019c1ff6-d89b-7e9b-8866-339601e9c067" xlink:to="loc_us-gaap_AccumulatedTranslationAdjustmentMember_019db6d8-acff-7c91-bce9-565d4b7d87ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_019c1ff6-d89b-77fc-9a33-87f9029d6f60" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019c1ff6-d89b-7e9b-8866-339601e9c067" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_019c1ff6-d89b-77fc-9a33-87f9029d6f60" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019c1ff6-d89b-72e4-ac65-6395e364a747" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_019c1ff6-d89b-7dc1-8895-6c3d8e1c4acb" xlink:to="loc_us-gaap_Revenues_019c1ff6-d89b-72e4-ac65-6395e364a747" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_019c1ff6-d89b-7ba2-8033-c48bf84034e3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_019c1ff6-d89b-7dc1-8895-6c3d8e1c4acb" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_019c1ff6-d89b-7ba2-8033-c48bf84034e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating_019c1ff6-d89b-71b6-9a86-18637b5a0554" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestExpenseNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_019c1ff6-d89b-7dc1-8895-6c3d8e1c4acb" xlink:to="loc_us-gaap_InterestExpenseNonoperating_019c1ff6-d89b-71b6-9a86-18637b5a0554" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_019c1ff6-d89b-7b93-83e8-dee326145066" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_019c1ff6-d89b-7dc1-8895-6c3d8e1c4acb" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_019c1ff6-d89b-7b93-83e8-dee326145066" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019c1ff6-d89b-7692-b8a5-d726d5f2ab30" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_019c1ff6-d89b-7dc1-8895-6c3d8e1c4acb" xlink:to="loc_us-gaap_NetIncomeLoss_019c1ff6-d89b-7692-b8a5-d726d5f2ab30" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/SupplementalInformationRelatedPartyTransactionsDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#SupplementalInformationRelatedPartyTransactionsDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/SupplementalInformationRelatedPartyTransactionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_019c1ff6-d89b-7d0a-a70c-bf730ea44047" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019c1ff6-d89b-721e-ae17-b0db75e9de56" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019c1ff6-d89b-7d0a-a70c-bf730ea44047" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019c1ff6-d89b-721e-ae17-b0db75e9de56" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019c1ff6-d89b-7296-b251-675e59d3d9f2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019c1ff6-d89b-721e-ae17-b0db75e9de56" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019c1ff6-d89b-7296-b251-675e59d3d9f2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019c1ff6-d89b-7296-b251-675e59d3d9f2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019c1ff6-d89b-7296-b251-675e59d3d9f2" xlink:to="loc_us-gaap_RelatedPartyDomain_019c1ff6-d89b-7296-b251-675e59d3d9f2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019c1ff6-d89b-77b0-9637-9b40cdcaf8f1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019c1ff6-d89b-7296-b251-675e59d3d9f2" xlink:to="loc_us-gaap_RelatedPartyDomain_019c1ff6-d89b-77b0-9637-9b40cdcaf8f1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_019c1ff6-d89b-7377-8d40-9f1975bcd623" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019c1ff6-d89b-77b0-9637-9b40cdcaf8f1" xlink:to="loc_us-gaap_RelatedPartyMember_019c1ff6-d89b-7377-8d40-9f1975bcd623" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_019c1ff6-d89b-7d19-9cbb-cca1575b42aa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019c1ff6-d89b-721e-ae17-b0db75e9de56" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_019c1ff6-d89b-7d19-9cbb-cca1575b42aa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019c1ff6-d89b-7d19-9cbb-cca1575b42aa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019c1ff6-d89b-7d19-9cbb-cca1575b42aa" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019c1ff6-d89b-7d19-9cbb-cca1575b42aa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019c1ff6-d89b-778f-8988-faa5d688ca54" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019c1ff6-d89b-7d19-9cbb-cca1575b42aa" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019c1ff6-d89b-778f-8988-faa5d688ca54" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_LuAnCleanEnergyCompanyTransactionMember_019c1ff6-d89b-752c-a351-91c3431416a8" xlink:href="apd-20260331.xsd#apd_LuAnCleanEnergyCompanyTransactionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_019c1ff6-d89b-778f-8988-faa5d688ca54" xlink:to="loc_apd_LuAnCleanEnergyCompanyTransactionMember_019c1ff6-d89b-752c-a351-91c3431416a8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAmountsOfTransaction_019c1ff6-d89b-7c2f-8111-5be2898a0c3a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionAmountsOfTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019c1ff6-d89b-7d0a-a70c-bf730ea44047" xlink:to="loc_us-gaap_RelatedPartyTransactionAmountsOfTransaction_019c1ff6-d89b-7c2f-8111-5be2898a0c3a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_019c1ff6-d89b-74ed-8e46-40b8daab37e0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019c1ff6-d89b-7d0a-a70c-bf730ea44047" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_019c1ff6-d89b-74ed-8e46-40b8daab37e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtAndCapitalLeaseObligations_019c1ff6-d89b-7b69-8cab-2a22d1c2c049" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtAndCapitalLeaseObligations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019c1ff6-d89b-7d0a-a70c-bf730ea44047" xlink:to="loc_us-gaap_DebtAndCapitalLeaseObligations_019c1ff6-d89b-7b69-8cab-2a22d1c2c049" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtAndCapitalLeaseObligationsCurrent_019c1ff6-d89b-7bbc-98a6-dbf19ff6def2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtAndCapitalLeaseObligationsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019c1ff6-d89b-7d0a-a70c-bf730ea44047" xlink:to="loc_us-gaap_LongTermDebtAndCapitalLeaseObligationsCurrent_019c1ff6-d89b-7bbc-98a6-dbf19ff6def2" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/SupplementalInformationShareholderActivismRelatedCostsDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#SupplementalInformationShareholderActivismRelatedCostsDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/SupplementalInformationShareholderActivismRelatedCostsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_019d8990-be61-7d1d-8083-e7d60d251c59" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019d8990-be61-70bd-b620-9c5f7f2c6dd8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019d8990-be61-7d1d-8083-e7d60d251c59" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019d8990-be61-70bd-b620-9c5f7f2c6dd8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_019d8990-be61-73c9-a368-5e768401fb12" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_019d8990-be61-70bd-b620-9c5f7f2c6dd8" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_019d8990-be61-73c9-a368-5e768401fb12" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_019d8990-be61-73c9-a368-5e768401fb12_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_019d8990-be61-73c9-a368-5e768401fb12" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_019d8990-be61-73c9-a368-5e768401fb12_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_019d8990-be61-7100-bbeb-25d48fe70a53" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_019d8990-be61-73c9-a368-5e768401fb12" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_019d8990-be61-7100-bbeb-25d48fe70a53" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_ExecutiveSeparationCostsMember_019d8996-41e5-75c5-a15f-14628c512f49" xlink:href="apd-20260331.xsd#apd_ExecutiveSeparationCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_019d8990-be61-7100-bbeb-25d48fe70a53" xlink:to="loc_apd_ExecutiveSeparationCostsMember_019d8996-41e5-75c5-a15f-14628c512f49" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_ShareholderActivismCosts_019d8990-be61-7afa-810e-eef7730083a8" xlink:href="apd-20260331.xsd#apd_ShareholderActivismCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019d8990-be61-7d1d-8083-e7d60d251c59" xlink:to="loc_apd_ShareholderActivismCosts_019d8990-be61-7afa-810e-eef7730083a8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_ShareholderActivismCostsNetOfTax_019d8990-be61-7969-87f1-78f36f714b52" xlink:href="apd-20260331.xsd#apd_ShareholderActivismCostsNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019d8990-be61-7d1d-8083-e7d60d251c59" xlink:to="loc_apd_ShareholderActivismCostsNetOfTax_019d8990-be61-7969-87f1-78f36f714b52" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAcceleratedCompensationCost_019d8990-be61-77b3-b079-65d2b54935cb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAcceleratedCompensationCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019d8990-be61-7d1d-8083-e7d60d251c59" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAcceleratedCompensationCost_019d8990-be61-77b3-b079-65d2b54935cb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeveranceCosts1_019d8990-be61-704d-9c6c-304437b86b24" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SeveranceCosts1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_019d8990-be61-7d1d-8083-e7d60d251c59" xlink:to="loc_us-gaap_SeveranceCosts1_019d8990-be61-704d-9c6c-304437b86b24" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/SupplementalInformationChangesinEstimatesDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#SupplementalInformationChangesinEstimatesDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/SupplementalInformationChangesinEstimatesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ChangeInAccountingEstimateLineItems_019c1ff6-d89b-7f9a-90f9-3298ae0e4c59" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ChangeInAccountingEstimateLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfChangeInAccountingEstimateTable_019c1ff6-d89b-76c0-8fd5-9a02ee88a1a9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfChangeInAccountingEstimateTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ChangeInAccountingEstimateLineItems_019c1ff6-d89b-7f9a-90f9-3298ae0e4c59" xlink:to="loc_us-gaap_ScheduleOfChangeInAccountingEstimateTable_019c1ff6-d89b-76c0-8fd5-9a02ee88a1a9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ChangeInAccountingEstimateByTypeAxis_019c1ff6-d89b-72fa-b983-b6483a076512" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ChangeInAccountingEstimateByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfChangeInAccountingEstimateTable_019c1ff6-d89b-76c0-8fd5-9a02ee88a1a9" xlink:to="loc_us-gaap_ChangeInAccountingEstimateByTypeAxis_019c1ff6-d89b-72fa-b983-b6483a076512" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_019c1ff6-d89b-72fa-b983-b6483a076512_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ChangeInAccountingEstimateTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ChangeInAccountingEstimateByTypeAxis_019c1ff6-d89b-72fa-b983-b6483a076512" xlink:to="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_019c1ff6-d89b-72fa-b983-b6483a076512_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_019c1ff6-d89b-7e28-87f9-be5f254d6d15" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ChangeInAccountingEstimateTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ChangeInAccountingEstimateByTypeAxis_019c1ff6-d89b-72fa-b983-b6483a076512" xlink:to="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_019c1ff6-d89b-7e28-87f9-be5f254d6d15" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractsAccountedForUnderPercentageOfCompletionMember_019c1ff6-d89b-7882-94fa-900153c679f1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractsAccountedForUnderPercentageOfCompletionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_019c1ff6-d89b-7e28-87f9-be5f254d6d15" xlink:to="loc_us-gaap_ContractsAccountedForUnderPercentageOfCompletionMember_019c1ff6-d89b-7882-94fa-900153c679f1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_019c1ff6-d89b-7290-b6e4-ad202778acf9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ChangeInAccountingEstimateLineItems_019c1ff6-d89b-7f9a-90f9-3298ae0e4c59" xlink:to="loc_us-gaap_OperatingIncomeLoss_019c1ff6-d89b-7290-b6e4-ad202778acf9" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/BusinessSegmentInformationScheduleofSegmentReportingInformationDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#BusinessSegmentInformationScheduleofSegmentReportingInformationDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/BusinessSegmentInformationScheduleofSegmentReportingInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019c1ff6-d958-7d0a-bf90-ae085d149afa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019c1ff6-d958-7342-8425-3240fca03192" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019c1ff6-d958-7d0a-bf90-ae085d149afa" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019c1ff6-d958-7342-8425-3240fca03192" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019c1ff6-d958-7a44-ae83-cc1faf6f316b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019c1ff6-d958-7342-8425-3240fca03192" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019c1ff6-d958-7a44-ae83-cc1faf6f316b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019c1ff6-d958-7a44-ae83-cc1faf6f316b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019c1ff6-d958-7a44-ae83-cc1faf6f316b" xlink:to="loc_us-gaap_SegmentDomain_019c1ff6-d958-7a44-ae83-cc1faf6f316b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019c1ff6-d958-74bc-b473-59390e1294b3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019c1ff6-d958-7a44-ae83-cc1faf6f316b" xlink:to="loc_us-gaap_SegmentDomain_019c1ff6-d958-74bc-b473-59390e1294b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_AmericasSegmentMember_019c1ff6-d958-7393-a0b0-d91325655281" xlink:href="apd-20260331.xsd#apd_AmericasSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019c1ff6-d958-74bc-b473-59390e1294b3" xlink:to="loc_apd_AmericasSegmentMember_019c1ff6-d958-7393-a0b0-d91325655281" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_AsiaSegmentMember_019c1ff6-d958-7d9c-b528-3b371c317efb" xlink:href="apd-20260331.xsd#apd_AsiaSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019c1ff6-d958-74bc-b473-59390e1294b3" xlink:to="loc_apd_AsiaSegmentMember_019c1ff6-d958-7d9c-b528-3b371c317efb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_EuropeSegmentMember_019c1ff6-d958-7de6-882e-da255c90a347" xlink:href="apd-20260331.xsd#apd_EuropeSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019c1ff6-d958-74bc-b473-59390e1294b3" xlink:to="loc_apd_EuropeSegmentMember_019c1ff6-d958-7de6-882e-da255c90a347" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_MiddleEastAndIndiaSegmentMember_019c1ff6-d958-729d-8bb6-803b828162d2" xlink:href="apd-20260331.xsd#apd_MiddleEastAndIndiaSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019c1ff6-d958-74bc-b473-59390e1294b3" xlink:to="loc_apd_MiddleEastAndIndiaSegmentMember_019c1ff6-d958-729d-8bb6-803b828162d2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateAndOtherMember_019c1ff6-d958-7045-b837-2f85f4ad852d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateAndOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019c1ff6-d958-74bc-b473-59390e1294b3" xlink:to="loc_us-gaap_CorporateAndOtherMember_019c1ff6-d958-7045-b837-2f85f4ad852d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019c1ff6-d958-7c8d-9e75-73e319d2f4f0" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019c1ff6-d958-7342-8425-3240fca03192" xlink:to="loc_srt_ConsolidationItemsAxis_019c1ff6-d958-7c8d-9e75-73e319d2f4f0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019c1ff6-d958-7c8d-9e75-73e319d2f4f0_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019c1ff6-d958-7c8d-9e75-73e319d2f4f0" xlink:to="loc_srt_ConsolidationItemsDomain_019c1ff6-d958-7c8d-9e75-73e319d2f4f0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019c1ff6-d958-7d3e-9197-8baf07ba3779" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019c1ff6-d958-7c8d-9e75-73e319d2f4f0" xlink:to="loc_srt_ConsolidationItemsDomain_019c1ff6-d958-7d3e-9197-8baf07ba3779" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019c1ff6-d958-7f57-94e9-115d605e9b96" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019c1ff6-d958-7d3e-9197-8baf07ba3779" xlink:to="loc_us-gaap_OperatingSegmentsMember_019c1ff6-d958-7f57-94e9-115d605e9b96" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019c1ff6-d958-7411-a630-8820829d1e45" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019c1ff6-d958-7d0a-bf90-ae085d149afa" xlink:to="loc_us-gaap_Revenues_019c1ff6-d958-7411-a630-8820829d1e45" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_019c1ff6-d958-71ca-aee1-91bde49197f7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019c1ff6-d958-7d0a-bf90-ae085d149afa" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_019c1ff6-d958-71ca-aee1-91bde49197f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_019c1ff6-d958-703e-8795-70d42cf91c80" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019c1ff6-d958-7d0a-bf90-ae085d149afa" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_019c1ff6-d958-703e-8795-70d42cf91c80" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherItemAmount_019c1ff6-d958-7855-9089-fb5ab3bac0e9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingOtherItemAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019c1ff6-d958-7d0a-bf90-ae085d149afa" xlink:to="loc_us-gaap_SegmentReportingOtherItemAmount_019c1ff6-d958-7855-9089-fb5ab3bac0e9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_019c1ff6-d958-79e2-abeb-7b118f61cdb4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019c1ff6-d958-7d0a-bf90-ae085d149afa" xlink:to="loc_us-gaap_OperatingIncomeLoss_019c1ff6-d958-79e2-abeb-7b118f61cdb4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_019c1ff6-d958-7451-88ab-198003491827" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019c1ff6-d958-7d0a-bf90-ae085d149afa" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_019c1ff6-d958-7451-88ab-198003491827" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_019c1ff6-d958-74ab-bc45-c86d2bbbf227" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019c1ff6-d958-7d0a-bf90-ae085d149afa" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_019c1ff6-d958-74ab-bc45-c86d2bbbf227" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_019c1ff6-d958-7a47-8afe-861c67947f4e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentExpenditureAdditionToLongLivedAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019c1ff6-d958-7d0a-bf90-ae085d149afa" xlink:to="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_019c1ff6-d958-7a47-8afe-861c67947f4e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures_019c1ff6-d958-79d1-b9ca-9a59597f8212" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019c1ff6-d958-7d0a-bf90-ae085d149afa" xlink:to="loc_us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures_019c1ff6-d958-79d1-b9ca-9a59597f8212" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_019c1ff6-d958-71c6-8747-3681da3a52a2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019c1ff6-d958-7d0a-bf90-ae085d149afa" xlink:to="loc_us-gaap_Assets_019c1ff6-d958-71c6-8747-3681da3a52a2" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.airproducts.com/role/BusinessSegmentInformationReconciliationofSegmentOperatingIncometoConsolidatedResultsDetails" xlink:type="simple" xlink:href="apd-20260331.xsd#BusinessSegmentInformationReconciliationofSegmentOperatingIncometoConsolidatedResultsDetails"/>
  <link:definitionLink xlink:role="http://www.airproducts.com/role/BusinessSegmentInformationReconciliationofSegmentOperatingIncometoConsolidatedResultsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019c1ff6-d958-7716-bce5-98b363b5d68a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019c1ff6-d958-7eb2-9c8a-fc55fc3d444a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019c1ff6-d958-7716-bce5-98b363b5d68a" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019c1ff6-d958-7eb2-9c8a-fc55fc3d444a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_019c1ff6-d958-73b7-a367-87b03958ab86" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019c1ff6-d958-7eb2-9c8a-fc55fc3d444a" xlink:to="loc_srt_ConsolidationItemsAxis_019c1ff6-d958-73b7-a367-87b03958ab86" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019c1ff6-d958-73b7-a367-87b03958ab86_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_019c1ff6-d958-73b7-a367-87b03958ab86" xlink:to="loc_srt_ConsolidationItemsDomain_019c1ff6-d958-73b7-a367-87b03958ab86_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_019c1ff6-d958-7384-b5f4-3b7fef1571dc" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_019c1ff6-d958-73b7-a367-87b03958ab86" xlink:to="loc_srt_ConsolidationItemsDomain_019c1ff6-d958-7384-b5f4-3b7fef1571dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_019c1ff6-d958-7dd8-8e99-749d5e67d1b4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019c1ff6-d958-7384-b5f4-3b7fef1571dc" xlink:to="loc_us-gaap_OperatingSegmentsMember_019c1ff6-d958-7dd8-8e99-749d5e67d1b4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MaterialReconcilingItemsMember_019c1ff6-d958-7be4-a428-509fc8e6b66c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MaterialReconcilingItemsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_019c1ff6-d958-7384-b5f4-3b7fef1571dc" xlink:to="loc_us-gaap_MaterialReconcilingItemsMember_019c1ff6-d958-7be4-a428-509fc8e6b66c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_019c1ff6-d958-7a43-8262-10aa4db04f40" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019c1ff6-d958-7716-bce5-98b363b5d68a" xlink:to="loc_us-gaap_OperatingIncomeLoss_019c1ff6-d958-7a43-8262-10aa4db04f40" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_019c1ff6-d958-73d3-93d8-72e4a45907a5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019c1ff6-d958-7716-bce5-98b363b5d68a" xlink:to="loc_us-gaap_RestructuringCharges_019c1ff6-d958-73d3-93d8-72e4a45907a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_apd_ShareholderActivismCosts_019c1ff6-d958-77b2-b253-8dca0e5a3c76" xlink:href="apd-20260331.xsd#apd_ShareholderActivismCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019c1ff6-d958-7716-bce5-98b363b5d68a" xlink:to="loc_apd_ShareholderActivismCosts_019c1ff6-d958-77b2-b253-8dca0e5a3c76" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_019c1ff6-d958-724f-ad43-13567bdd9ac5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019c1ff6-d958-7716-bce5-98b363b5d68a" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_019c1ff6-d958-724f-ad43-13567bdd9ac5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating_019c1ff6-d958-7eed-885a-80fbc7591fc4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestExpenseNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019c1ff6-d958-7716-bce5-98b363b5d68a" xlink:to="loc_us-gaap_InterestExpenseNonoperating_019c1ff6-d958-7eed-885a-80fbc7591fc4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_019c1ff6-d958-7512-ac0e-7489df5dde7f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019c1ff6-d958-7716-bce5-98b363b5d68a" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_019c1ff6-d958-7512-ac0e-7489df5dde7f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019c1ff6-d958-7425-b417-6cca5da50cfc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019c1ff6-d958-7716-bce5-98b363b5d68a" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019c1ff6-d958-7425-b417-6cca5da50cfc" xlink:type="arc" order="6"/>
  </link:definitionLink>
</link:linkbase>
