<?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>0009 - Disclosure - Summary of Significant Accounting Policies</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>2</Level><ElementName>us-gaap_SignificantAccountingPoliciesTextBlock</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="From2013-01-01to2013-06-30" UnitID=""><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText>&lt;div style="text-indent: 0pt; display: block"&gt;&lt;font style="display: inline; font: bold 10pt Times New Roman"&gt;Note 3 &amp;#8211; Summary of Significant Accounting Policies&lt;/font&gt;&lt;/div&gt;

&lt;div style="text-indent: 0pt; display: block"&gt;&lt;br /&gt;
&lt;/div&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt; text-align: justify"&gt;&lt;font style="font: italic bold 10pt Times New Roman; display: inline"&gt;Principles of Consolidation&lt;/font&gt;&lt;/div&gt;

&lt;div style="text-indent: 0pt; display: block"&gt;&lt;br /&gt;
&lt;/div&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt; text-align: justify"&gt;&lt;font style="display: inline; font: 10pt Times New Roman"&gt;The condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries, Echo Automotive, LLC and Advanced Technical Asset Holdings, LLC, beginning with their respective dates of acquisition. All significant intercompany accounts and transactions have been eliminated.&lt;/font&gt;&lt;/div&gt;

&lt;div style="text-indent: 0pt; display: block"&gt;&lt;br /&gt;
&lt;/div&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt; text-align: justify"&gt;&lt;font style="font: italic bold 10pt Times New Roman; display: inline"&gt;Fair Value&lt;/font&gt;&lt;/div&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt; text-align: justify"&gt;&amp;#160;&lt;/div&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt; text-align: justify"&gt;&lt;font style="display: inline; font: 10pt Times New Roman"&gt;Fair value is the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. As required by the Fair Value Measurements and Disclosures Topic of the FASB ASC (&amp;#8220;ASC 820-10&amp;#8221;), fair value is measured based on a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value. When determining fair value, the Company considers the principal or most advantageous market in which it would transact, and it considers assumptions that market participants would use when pricing the asset or liability.&lt;/font&gt;&lt;/div&gt;

&lt;div style="text-indent: 0pt; display: block"&gt;&lt;br /&gt;
&lt;/div&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt; text-align: justify"&gt;&lt;font style="display: inline; font: 10pt Times New Roman"&gt;The three levels of inputs that may be used to measure fair value are as follows:&lt;/font&gt;&lt;/div&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt; text-align: justify"&gt;&lt;font style="display: inline; font: 10pt Times New Roman"&gt;&amp;#160;&lt;/font&gt;&lt;/div&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt; text-align: justify"&gt;&lt;font style="display: inline; font: 10pt Times New Roman"&gt;Level 1. Quoted prices in active markets for identical assets or liabilities.&lt;/font&gt;&lt;/div&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt; text-align: justify"&gt;&amp;#160;&lt;/div&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt; text-align: justify"&gt;&lt;font style="display: inline; font: 10pt Times New Roman"&gt;Level 2. Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in markets with insufficient volume or infrequent transactions (less active markets), inputs that are other than quoted prices that are observable for the asset or liability or market corroborated inputs.&lt;/font&gt;&lt;/div&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt; text-align: justify"&gt;&amp;#160;&lt;/div&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt; text-align: justify"&gt;&lt;font style="display: inline; font: 10pt Times New Roman"&gt;Level 3. Unobservable inputs to the valuation methodology that are significant to the measurement of the fair value of assets or liabilities, which may include internal data or valuation data received from the security issuer.&lt;/font&gt;&lt;/div&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt; text-align: justify"&gt;&amp;#160;&lt;/div&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 0pt; text-align: justify"&gt;&lt;font style="display: inline; font: 10pt Times New Roman"&gt;The Company&amp;#8217;s financial instruments include cash, accounts payable, accrued liabilities, related party advances, and notes payable. The carrying value of these instruments approximates fair value due to the short-term nature of such instruments. The Company used inputs that would qualify as Level 2 inputs to make its assessment of the approximate fair value of the notes payable.&lt;/font&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 all significant accounting policies of the reporting entity.</ElementDefenition><ElementReferences>Reference 1: http://www.xbrl.org/2003/role/presentationRef

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