<?xml version="1.0" encoding="us-ascii"?><InstanceReport xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"><Version>2.4.0.8</Version><ReportLongName>2101100 - Disclosure - Basis of Presentation</ReportLongName><DisplayLabelColumn>true</DisplayLabelColumn><ShowElementNames>false</ShowElementNames><RoundingOption /><HasEmbeddedReports>false</HasEmbeddedReports><Columns><Column FlagID="0"><Id>1</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelSeparator>

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</LabelSeparator><Level>1</Level><ElementName>us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract</ElementName><ElementPrefix>us-gaap_</ElementPrefix><IsBaseElement>true</IsBaseElement><BalanceType>na</BalanceType><PeriodType>duration</PeriodType><IsReportTitle>false</IsReportTitle><IsSegmentTitle>false</IsSegmentTitle><IsCalendarTitle>false</IsCalendarTitle><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><FootnoteIndexer /><Cells><Cell FlagID="0" ContextID="" UnitID=""><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText /><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat></Cell></Cells><ElementDataType>xbrli:stringItemType</ElementDataType><SimpleDataType>string</SimpleDataType><IsTotalLabel>false</IsTotalLabel><UnitID>0</UnitID><Label>Organization, Consolidation and Presentation of Financial Statements [Abstract]</Label></Row><Row FlagID="0"><Id>2</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelSeparator>

</LabelSeparator><Level>2</Level><ElementName>us-gaap_BasisOfPresentationAndSignificantAccountingPoliciesTextBlock</ElementName><ElementPrefix>us-gaap_</ElementPrefix><IsBaseElement>true</IsBaseElement><BalanceType>na</BalanceType><PeriodType>duration</PeriodType><IsReportTitle>false</IsReportTitle><IsSegmentTitle>false</IsSegmentTitle><IsCalendarTitle>false</IsCalendarTitle><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><PreferredLabelRole>terseLabel</PreferredLabelRole><FootnoteIndexer /><Cells><Cell FlagID="0" ContextID="D2014Q1" UnitID=""><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText>&lt;div style="font-family:Times New Roman;font-size:10pt;"&gt;&lt;div style="line-height:120%;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;font-weight:bold;"&gt;Basis of Presentation&lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;text-align:justify;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;The accompanying unaudited Condensed Consolidated Financial Statements of Rentrak Corporation have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (&amp;#8220;SEC&amp;#8221;).  Certain information and footnote disclosures normally included in financial statements prepared in accordance with the accounting principles generally accepted in the United States of America have been condensed or omitted pursuant to such rules and regulations.  The results of operations for the three month period ended &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;June&amp;#160;30, 2013&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; are not necessarily indicative of the results to be expected for the entire fiscal year ending &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;March&amp;#160;31, 2014&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; (&amp;#8220;Fiscal &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;2014&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;&amp;#8221;).  The Condensed Consolidated Financial Statements should be read in conjunction with the Consolidated Financial Statements and footnotes thereto included in our &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;2013&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; Annual Report on Form 10-K (the &amp;#8220;Form 10-K&amp;#8221;).&lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;text-align:justify;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;&lt;br clear="none"/&gt;&lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;text-align:justify;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;The Condensed Consolidated Financial Statements reflect, in the opinion of management, all material adjustments (which include only normal recurring adjustments) necessary to present fairly our financial position, results of operations and cash flows. &lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;text-align:justify;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;&lt;br clear="none"/&gt;&lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;text-align:justify;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;font-style:italic;font-weight:bold;"&gt;Principles of Consolidation&lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;text-align:justify;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;&lt;br clear="none"/&gt;&lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;text-align:justify;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;The Condensed Consolidated Financial Statements include the accounts of Rentrak Corporation and its wholly owned subsidiaries, and those entities in which we have a controlling interest.  All intercompany accounts and transactions have been eliminated in consolidation. &lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;text-align:justify;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;&lt;br clear="none"/&gt;&lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;text-align:justify;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;In Fiscal 2012, we established a Chinese joint venture, Sinotrak, and hold a &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;font-style:normal;text-decoration:none;"&gt;49%&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; ownership interest in this variable interest entity (&amp;#8220;VIE&amp;#8221;).  Sinotrak has been included in our Condensed Consolidated Financial Statements, as we have determined that we are the primary beneficiary of the VIE, given our significant influence over day to day operations among other factors.  To date, the activities of Sinotrak have been limited primarily to initial cash contributions from both joint venture parties and costs associated with Sinotrak&amp;#8217;s formation.  The equity interests of the noncontrolling  party, totaling &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;$1.0 million&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; as of &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;June&amp;#160;30, 2013&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;, are reported as a noncontrolling interest in our Condensed Consolidated Balance Sheets.  The noncontrolling party&amp;#8217;s share of the expenses for the three months ended June 30, 2013, are included in net loss attributable to noncontrolling interest on our Condensed Consolidated Statements of Operations.&lt;/font&gt;&lt;/div&gt;&lt;/div&gt;</NonNumbericText><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat></Cell></Cells><ElementDataType>nonnum:textBlockItemType</ElementDataType><SimpleDataType>na</SimpleDataType><ElementDefenition>The entire disclosure for the basis of presentation and significant accounting policies concepts. Basis of presentation describes the underlying basis used to prepare the financial statements (for example, US Generally Accepted Accounting Principles, Other Comprehensive Basis of Accounting, IFRS).  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