<?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>1020 - 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>

</LabelSeparator><CurrencyCode /><FootnoteIndexer /><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios><MCU><KeyName /><CurrencySymbol /><contextRef><ContextID>D2013Q2YTD</ContextID><EntitySchema>http://www.sec.gov/CIK</EntitySchema><EntityValue>0001527705</EntityValue><PeriodDisplayName /><PeriodType>duration</PeriodType><PeriodStartDate>2013-01-01T00:00:00</PeriodStartDate><PeriodEndDate>2013-06-30T00:00:00</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="Jun. 30, 2013" /></Labels></Column></Columns><Rows><Row FlagID="0"><Id>1</Id><IsAbstractGroupTitle>true</IsAbstractGroupTitle><LabelSeparator>

</LabelSeparator><Level>1</Level><ElementName>us-gaap_AccountingPoliciesAbstract</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>Summary of Significant Accounting Policies</Label></Row><Row FlagID="0"><Id>2</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelSeparator>

</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><PreferredLabelRole>terseLabel</PreferredLabelRole><FootnoteIndexer /><Cells><Cell FlagID="0" ContextID="D2013Q2YTD" UnitID=""><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText>&lt;div style="font-size:10.0pt;font-family:Times New Roman;"&gt;
&lt;p style="MARGIN: 0in 0in 0pt;"&gt;&lt;b&gt;&lt;font style="FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold;" size="2"&gt;Note 2. Summary of Significant Accounting Policies&lt;/font&gt;&lt;/b&gt;&lt;/p&gt;
&lt;p style="MARGIN: 0in 0in 0pt;"&gt;&amp;#160;&lt;/p&gt;
&lt;p style="TEXT-INDENT: 0.5in; MARGIN: 0in 0in 0pt;"&gt;&lt;i&gt;&lt;font style="FONT-STYLE: italic; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt;" size="2"&gt;Basis of Presentation&lt;/font&gt;&lt;/i&gt;&lt;/p&gt;
&lt;p style="TEXT-INDENT: 0.5in; MARGIN: 0in 0in 0pt;"&gt;&amp;#160;&lt;/p&gt;
&lt;p style="TEXT-INDENT: 0.5in; MARGIN: 0in 0in 0pt;"&gt;&lt;font style="FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt;" size="2"&gt;The accompanying condensed financial statements have been prepared, without audit, pursuant to the rules&amp;#160;and regulations of the Securities and Exchange Commission. Certain information and footnote disclosures normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States have been condensed or omitted pursuant to such rules&amp;#160;and regulations, although we believe that the disclosures are adequate to make the information presented not misleading.&amp;#160; In the opinion of management, all adjustments (which include normal recurring adjustments) necessary for a fair presentation of the results of the Company&amp;#8217;s financial position, results of operations and cash flows for the interim periods have been made.&amp;#160; The interim results reflected in these condensed financial statements are not necessarily indicative of results to be expected for the full fiscal year.&amp;#160; The accompanying condensed financial statements should be read in conjunction with the financial statements and notes thereto included in the Company&amp;#8217;s Annual Report on Form&amp;#160;10-K for the year ended December&amp;#160;31, 2012.&lt;/font&gt;&lt;/p&gt;
&lt;p style="TEXT-INDENT: 0.5in; MARGIN: 0in 0in 0pt;"&gt;&amp;#160;&lt;/p&gt;
&lt;p style="TEXT-INDENT: 0.5in; MARGIN: 0in 0in 0pt;"&gt;&lt;i&gt;&lt;font style="FONT-STYLE: italic; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt;" size="2"&gt;Principles of Consolidation&lt;/font&gt;&lt;/i&gt;&lt;/p&gt;
&lt;p style="TEXT-INDENT: 0.5in; MARGIN: 0in 0in 0pt;"&gt;&amp;#160;&lt;/p&gt;
&lt;p style="TEXT-INDENT: 0.5in; MARGIN: 0in 0in 0pt;"&gt;&lt;font style="FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt;" size="2"&gt;The accompanying condensed financial statements include the Company and its wholly owned subsidiary, Aliante Gaming.&amp;#160; All material intercompany transactions are eliminated in consolidation.&lt;/font&gt;&lt;/p&gt;
&lt;p style="TEXT-INDENT: 0.3in; MARGIN: 0in 0in 0pt 0.2in;"&gt;&amp;#160;&lt;/p&gt;
&lt;p style="TEXT-INDENT: 0.3in; MARGIN: 0in 0in 0pt 0.2in;"&gt;&lt;i&gt;&lt;font style="FONT-STYLE: italic; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt;" size="2"&gt;Fair Value of Financial Instruments&lt;/font&gt;&lt;/i&gt;&lt;/p&gt;
&lt;p style="TEXT-INDENT: 0.3in; MARGIN: 0in 0in 0pt 0.2in;"&gt;&amp;#160;&lt;/p&gt;
&lt;p style="TEXT-INDENT: 0.5in; MARGIN: 0in 0in 0pt;"&gt;&lt;font style="FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt;" size="2"&gt;The estimated fair value of the Company&amp;#8217;s financial instruments has been determined by the Company using available market information and valuation methodologies. However, considerable judgment is required to develop the estimates of fair value; thus, the estimates provided herein are not necessarily indicative of the amounts that the Company could realize in a current market exchange.&lt;/font&gt;&lt;/p&gt;
&lt;p style="TEXT-INDENT: 0.5in; MARGIN: 0in 0in 0pt;"&gt;&amp;#160;&lt;/p&gt;
&lt;p style="TEXT-INDENT: 0.5in; MARGIN: 0in 0in 0pt;"&gt;&lt;font style="FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt;" size="2"&gt;The carrying amounts of cash, receivables, accounts payable and accrued expenses approximate fair value because of the short-term nature of these instruments.&lt;/font&gt;&lt;/p&gt;
&lt;p style="TEXT-INDENT: 0.5in; MARGIN: 0in 0in 0pt;"&gt;&amp;#160;&lt;/p&gt;
&lt;p style="MARGIN: 0in 0in 0pt 0.5in;"&gt;&lt;i&gt;&lt;font style="FONT-STYLE: italic; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt;" size="2"&gt;Related Party Transactions&lt;/font&gt;&lt;/i&gt;&lt;/p&gt;
&lt;p style="MARGIN: 0in 0in 0pt 0.5in;"&gt;&amp;#160;&lt;/p&gt;
&lt;p style="TEXT-INDENT: 0.5in; MARGIN: 0in 0in 0pt;"&gt;&lt;font style="FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt;" size="2"&gt;On the Effective Date, the Company and Aliante Gaming entered into the Senior Secured Credit Facility with the Lenders, which own 100% of the Company&amp;#8217;s Common Units.&amp;#160; In addition, pursuant to the amended and restated operating agreement (the &amp;#8220;&lt;i&gt;Operating Agreement&amp;#8221;&lt;/i&gt;) the Lenders have the right to designate up to four individuals to serve on the Company&amp;#8217;s Board of Managers. The members of the Board of Managers that are designated by the Lenders could be deemed to have a material direct or indirect interest in the Senior Secured Credit Agreement by virtue of their relationship with the Lenders.&lt;/font&gt;&lt;/p&gt;
&lt;p style="MARGIN: 0in 0in 0pt;"&gt;&amp;#160;&lt;/p&gt;
&lt;p style="TEXT-INDENT: 0.5in; MARGIN: 0in 0in 0pt;"&gt;&lt;i&gt;&lt;font style="FONT-STYLE: italic; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt;" size="2"&gt;Income Taxes&lt;/font&gt;&lt;/i&gt;&lt;/p&gt;
&lt;p style="TEXT-INDENT: 0.5in; MARGIN: 0in 0in 0pt;"&gt;&amp;#160;&lt;/p&gt;
&lt;p style="TEXT-INDENT: 0.5in; MARGIN: 0in 0in 0pt;"&gt;&lt;font style="FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt;" size="2"&gt;We are a limited liability company disregarded as an entity separate from its owners for income tax purposes and as such, are a pass-through entity and not liable for income tax in the jurisdiction in which we operate. As a result, no provision for income taxes has been made in the accompanying condensed financial statements.&lt;/font&gt;&lt;/p&gt;
&lt;p style="TEXT-INDENT: 0.5in; MARGIN: 0in 0in 0pt;"&gt;&amp;#160;&lt;/p&gt;
&lt;p style="TEXT-INDENT: 0.5in; MARGIN: 0in 0in 0pt;"&gt;&lt;i&gt;&lt;font style="FONT-STYLE: italic; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt;" size="2"&gt;Recently Issued Accounting Standards&lt;/font&gt;&lt;/i&gt;&lt;/p&gt;
&lt;p style="TEXT-INDENT: 0.5in; MARGIN: 0in 0in 0pt;"&gt;&amp;#160;&lt;/p&gt;
&lt;p style="TEXT-INDENT: 0.5in; MARGIN: 0in 0in 0pt;"&gt;&lt;font style="FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt;" size="2"&gt;In December&amp;#160;2011, the Financial Accounting Standards Board &lt;i&gt;(&amp;#8220;FASB&amp;#8221;&lt;/i&gt;) issued amendments to enhance disclosures about offsetting and related arrangements. This information will enable the users of the financial statements to evaluate the effect or potential effect of netting arrangements on an entity&amp;#8217;s financial position, including the effect or potential effect of rights of setoff associated with certain financial and derivative instruments. These amendments are effective for annual reporting periods, and interim periods within those years, beginning on or after January&amp;#160;1, 2013. The disclosures required by these amendments should be provided retrospectively for all comparative periods presented. Management did not believe that these amendments will have a material impact on the financial statements.&lt;/font&gt;&lt;/p&gt;
&lt;p style="TEXT-ALIGN: center; MARGIN: 0in 0in 0pt;" align="center"&gt;&amp;#160;&lt;/p&gt;
&lt;p style="TEXT-INDENT: 0.5in; MARGIN: 0in 0in 0pt;"&gt;&lt;font style="FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt;" size="2"&gt;A variety of proposed or otherwise potential accounting standards are currently under study by standard-setting organizations and certain regulatory agencies. Because of the tentative and preliminary nature of such proposed standards, we have not yet determined the effect, if any, that the implementation of such proposed standards would have on our condensed financial statements.&lt;/font&gt;&lt;/p&gt;
&lt;p style="TEXT-INDENT: 0.5in; MARGIN: 0in 0in 0pt;"&gt;&amp;#160;&lt;/p&gt;
&lt;p style="TEXT-INDENT: 0.5in; MARGIN: 0in 0in 0pt;"&gt;&lt;i&gt;&lt;font style="FONT-STYLE: italic; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt;" size="2"&gt;Reclassifications&lt;/font&gt;&lt;/i&gt;&lt;/p&gt;
&lt;p style="TEXT-INDENT: 0.5in; MARGIN: 0in 0in 0pt;"&gt;&amp;#160;&lt;/p&gt;
&lt;p style="TEXT-INDENT: 0.5in; MARGIN: 0in 0in 0pt;"&gt;&lt;font style="FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt;" size="2"&gt;The financial statements reflect certain reclassifications to prior year amounts to conform the classification in the current period.&amp;#160; For the three and six month periods ended June&amp;#160;30 2012 we reclassified $0.2 million and $0.4 million, respectively, in expenses included in &amp;#8220;Selling, General&amp;#160;&amp;amp; Administrative&amp;#8221; to expenses included in &amp;#8220;Other Expenses&amp;#8221; as we believe these expenses are more closely associated with the other activities.&amp;#160; These reclassifications have no effect on previously reported operating income and net income.&lt;/font&gt;&lt;/p&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

 -Publisher FASB

 -Name Accounting Standards Codification

 -Topic 235

 -SubTopic 10

 -Section 50

 -Paragraph 3

 -URI http://asc.fasb.org/extlink&amp;oid=6367646&amp;loc=d3e18780-107790



Reference 2: http://www.xbrl.org/2003/role/presentationRef

 -Publisher FASB

 -Name Accounting Standards Codification

 -Topic 235

 -SubTopic 10

 -Section 50

 -Paragraph 1

 -URI http://asc.fasb.org/extlink&amp;oid=6367646&amp;loc=d3e18726-107790



Reference 3: http://www.xbrl.org/2003/role/presentationRef

 -Publisher FASB

 -Name Accounting Standards Codification

 -Topic 235

 -SubTopic 10

 -Section 50

 -Paragraph 6

 -URI http://asc.fasb.org/extlink&amp;oid=6367646&amp;loc=d3e18861-107790



Reference 4: http://www.xbrl.org/2003/role/presentationRef

 -Publisher FASB

 -Name Accounting Standards Codification

 -Topic 235

 -SubTopic 10

 -Section 50

 -Paragraph 2

 -URI http://asc.fasb.org/extlink&amp;oid=6367646&amp;loc=d3e18743-107790



Reference 5: http://www.xbrl.org/2003/role/presentationRef

 -Publisher FASB

 -Name Accounting Standards Codification

 -Topic 235

 -SubTopic 10

 -Section 50

 -Paragraph 5

 -URI http://asc.fasb.org/extlink&amp;oid=6367646&amp;loc=d3e18854-107790



</ElementReferences><IsTotalLabel>false</IsTotalLabel><UnitID>0</UnitID><Label>Summary of Significant Accounting Policies</Label></Row></Rows><Footnotes /><IsEquityReport>false</IsEquityReport><ReportName>Summary of Significant Accounting Policies</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://www.aliantecasinohotel.com/role/DisclosureSummaryOfSignificantAccountingPolicies</RoleURI><NumberOfCols>1</NumberOfCols><NumberOfRows>2</NumberOfRows></InstanceReport>
