<?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>001000 - 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>

</LabelSeparator><CurrencyCode /><FootnoteIndexer /><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios><MCU><KeyName /><CurrencySymbol /><contextRef><ContextID>FROM_Feb02_2013_TO_Aug02_2013</ContextID><EntitySchema>http://www.sec.gov/CIK</EntitySchema><EntityValue>0000060667</EntityValue><PeriodDisplayName /><PeriodType>duration</PeriodType><PeriodStartDate>2013-02-02T00:00:00</PeriodStartDate><PeriodEndDate>2013-08-02T00:00:00</PeriodEndDate><Segments /><Scenarios /></contextRef><UPS /><CurrencyCode /><OriginalCurrencyCode /></MCU><CurrencySymbol /><Labels><Label Key="CalendarSupplement" Id="0" Label="6 Months Ended" /><Label Key="Calendar" Id="1" Label="Aug. 02, 2013" /></Labels></Column></Columns><Rows><Row FlagID="0"><Id>1</Id><IsAbstractGroupTitle>true</IsAbstractGroupTitle><LabelSeparator>

</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>Basis of Presentation</Label></Row><Row FlagID="0"><Id>2</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelSeparator>

</LabelSeparator><Level>2</Level><ElementName>us-gaap_BasisOfAccounting</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>verboseLabel</PreferredLabelRole><FootnoteIndexer /><Cells><Cell FlagID="0" ContextID="FROM_Feb02_2013_TO_Aug02_2013" UnitID=""><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText>&lt;p style='margin-top:0pt; margin-bottom:0pt'&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;font-weight:bold;margin-left:0px;"&gt;Note &lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;font-weight:bold;"&gt;1&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;font-weight:bold;"&gt;:&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt; &lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;font-weight:bold;"&gt;Basis of Presentation&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt; - The accompanying &lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;c&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;onsolidated &lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;f&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;inancial &lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;s&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;tatements (&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;u&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;naudited)&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt; and&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt; notes &lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;to&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt; the&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt; consolidated financial statements &lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;(unaudited) &lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;are presented in accordance with the rules and regulations of the Securities and Exchange Commission and do not include all the disclosures normally required in annual consolidated financial statements prepared in accordance with accounting principles generally accepted in the United States of America&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;.  The consolidated financial statements (unaudited),&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt; in the opinion of management, contain all adjustments necessary to present fairly the financial position as of &lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;August 2, 2013&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;,&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt; &lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;and &lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;August 3, 2012&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;,&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt; &lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;and &lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;the results of operations&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt; and&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt; &lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;comprehensive income&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt; &lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;for the three&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt; &lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;and six&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt; &lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;months ended &lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;August 2, 2013&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;,&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt; and &lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;August 3, 2012&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt; and cash flows for the six&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt; months ended &lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;August 2, 2013&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;, and &lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;August 3, 2012&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;.&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;  &lt;/font&gt;&lt;/p&gt;&lt;p style='margin-top:0pt; margin-bottom:0pt'&gt;&amp;#160;&lt;/p&gt;&lt;p style='margin-top:0pt; margin-bottom:0pt'&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;margin-left:0px;"&gt;These interim &lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;consolidated f&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;inancial &lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;s&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;tatements&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt; (unaudited)&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt; should be read in conjunction with the audited &lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;consolidated &lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;financial statements and notes thereto included in t&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;he Lowe's Companies, Inc. (the Company&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;) Annual Report on Form 10-K for the fiscal year ended &lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;February 1, 2013&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt; (the Annual Report&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;). &lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt; &lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:11pt;"&gt;The financial results for the interim periods may not be indicative of the financial results for the entire fiscal year. &lt;/font&gt;&lt;/p&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 accounting, or basis of presentation, used to prepare the financial statements (for example, US Generally Accepted Accounting Principles, Other Comprehensive Basis of Accounting, IFRS).</ElementDefenition><ElementReferences>No definition available.</ElementReferences><IsTotalLabel>false</IsTotalLabel><UnitID>0</UnitID><Label>Basis of Presentation</Label></Row></Rows><Footnotes /><IsEquityReport>false</IsEquityReport><ReportName>Basis of Presentation</ReportName><MonetaryRoundingLevel>UnKnown</MonetaryRoundingLevel><SharesRoundingLevel>UnKnown</SharesRoundingLevel><PerShareRoundingLevel>UnKnown</PerShareRoundingLevel><ExchangeRateRoundingLevel>UnKnown</ExchangeRateRoundingLevel><HasCustomUnits>true</HasCustomUnits><IsEmbedReport>false</IsEmbedReport><IsMultiCurrency>false</IsMultiCurrency><ReportType>Sheet</ReportType><RoleURI>http://lowes.com/role/DisclosureBasisOfPresentation</RoleURI><NumberOfCols>1</NumberOfCols><NumberOfRows>2</NumberOfRows></InstanceReport>
