﻿<?xml version="1.0" encoding="utf-8"?>
<InstanceReport xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <Version>2.2.0.7</Version>
  <hasSegments>false</hasSegments>
  <ReportName>Variable Interest Entities</ReportName>
  <ReportLongName>0209 - Disclosure - Variable Interest Entities</ReportLongName>
  <DisplayLabelColumn>true</DisplayLabelColumn>
  <ShowElementNames>false</ShowElementNames>
  <RoundingOption />
  <HasEmbeddedReports>false</HasEmbeddedReports>
  <Columns>
    <Column>
      <LabelColumn>false</LabelColumn>
      <Id>1</Id>
      <Labels>
        <Label Id="1" Label="6 Months Ended" />
        <Label Id="2" Label="Jun. 30, 2010" />
      </Labels>
      <CurrencyCode>USD</CurrencyCode>
      <FootnoteIndexer />
      <hasSegments>false</hasSegments>
      <hasScenarios>false</hasScenarios>
      <Segments />
      <Scenarios />
      <Units>
        <Unit>
          <UnitID>USD</UnitID>
          <UnitType>Standard</UnitType>
          <StandardMeasure>
            <MeasureSchema>http://www.xbrl.org/2003/iso4217</MeasureSchema>
            <MeasureValue>USD</MeasureValue>
            <MeasureNamespace>iso4217</MeasureNamespace>
          </StandardMeasure>
          <Scale>0</Scale>
        </Unit>
        <Unit>
          <UnitID>USDEPS</UnitID>
          <UnitType>Divide</UnitType>
          <NumeratorMeasure>
            <MeasureSchema>http://www.xbrl.org/2003/iso4217</MeasureSchema>
            <MeasureValue>USD</MeasureValue>
            <MeasureNamespace>iso4217</MeasureNamespace>
          </NumeratorMeasure>
          <DenominatorMeasure>
            <MeasureSchema>http://www.xbrl.org/2003/instance</MeasureSchema>
            <MeasureValue>shares</MeasureValue>
            <MeasureNamespace>xbrli</MeasureNamespace>
          </DenominatorMeasure>
          <Scale>0</Scale>
        </Unit>
        <Unit>
          <UnitID>Shares</UnitID>
          <UnitType>Standard</UnitType>
          <StandardMeasure>
            <MeasureSchema>http://www.xbrl.org/2003/instance</MeasureSchema>
            <MeasureValue>shares</MeasureValue>
            <MeasureNamespace>xbrli</MeasureNamespace>
          </StandardMeasure>
          <Scale>0</Scale>
        </Unit>
      </Units>
      <CurrencySymbol>$</CurrencySymbol>
    </Column>
  </Columns>
  <Rows>
    <Row>
      <Id>2</Id>
      <Label>Variable Interest Entities [Abstract]</Label>
      <Level>0</Level>
      <ElementName>cse_VariableInterestEntitiesAbstract</ElementName>
      <ElementPrefix>cse</ElementPrefix>
      <IsBaseElement>false</IsBaseElement>
      <BalanceType>na</BalanceType>
      <PeriodType>duration</PeriodType>
      <ShortDefinition>Variable Interest Entities.</ShortDefinition>
      <IsReportTitle>false</IsReportTitle>
      <IsSegmentTitle>false</IsSegmentTitle>
      <IsSubReportEnd>false</IsSubReportEnd>
      <IsCalendarTitle>false</IsCalendarTitle>
      <IsTuple>false</IsTuple>
      <IsAbstractGroupTitle>true</IsAbstractGroupTitle>
      <IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow>
      <IsEquityAdjustmentRow>false</IsEquityAdjustmentRow>
      <IsBeginningBalance>false</IsBeginningBalance>
      <IsEndingBalance>false</IsEndingBalance>
      <IsReverseSign>false</IsReverseSign>
      <PreferredLabelRole />
      <IsEPS>false</IsEPS>
      <FootnoteIndexer />
      <Cells>
        <Cell>
          <Id>1</Id>
          <ShowCurrencySymbol>false</ShowCurrencySymbol>
          <IsNumeric>false</IsNumeric>
          <IsRatio>false</IsRatio>
          <DisplayZeroAsNone>false</DisplayZeroAsNone>
          <NumericAmount>0</NumericAmount>
          <RoundedNumericAmount>0</RoundedNumericAmount>
          <NonNumbericText />
          <NonNumericTextHeader />
          <FootnoteIndexer />
          <hasSegments>false</hasSegments>
          <hasScenarios>false</hasScenarios>
          <DisplayDateInUSFormat>false</DisplayDateInUSFormat>
        </Cell>
      </Cells>
      <OriginalInstanceReportColumns />
      <ElementDataType>xbrli:stringItemType</ElementDataType>
      <SimpleDataType>string</SimpleDataType>
      <ElementDefenition>Variable Interest Entities.</ElementDefenition>
      <IsTotalLabel>false</IsTotalLabel>
    </Row>
    <Row>
      <Id>3</Id>
      <Label>Variable Interest Entities</Label>
      <Level>1</Level>
      <ElementName>us-gaap_ScheduleOfVariableInterestEntitiesTextBlock</ElementName>
      <ElementPrefix>us-gaap</ElementPrefix>
      <IsBaseElement>true</IsBaseElement>
      <BalanceType>na</BalanceType>
      <PeriodType>duration</PeriodType>
      <ShortDefinition>No definition available.</ShortDefinition>
      <IsReportTitle>false</IsReportTitle>
      <IsSegmentTitle>false</IsSegmentTitle>
      <IsSubReportEnd>false</IsSubReportEnd>
      <IsCalendarTitle>false</IsCalendarTitle>
      <IsTuple>false</IsTuple>
      <IsAbstractGroupTitle>false</IsAbstractGroupTitle>
      <IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow>
      <IsEquityAdjustmentRow>false</IsEquityAdjustmentRow>
      <IsBeginningBalance>false</IsBeginningBalance>
      <IsEndingBalance>false</IsEndingBalance>
      <IsReverseSign>false</IsReverseSign>
      <PreferredLabelRole>verboselabel</PreferredLabelRole>
      <IsEPS>false</IsEPS>
      <FootnoteIndexer />
      <Cells>
        <Cell>
          <Id>1</Id>
          <ShowCurrencySymbol>false</ShowCurrencySymbol>
          <IsNumeric>false</IsNumeric>
          <IsRatio>false</IsRatio>
          <DisplayZeroAsNone>false</DisplayZeroAsNone>
          <NumericAmount>0</NumericAmount>
          <RoundedNumericAmount>0</RoundedNumericAmount>
          <NonNumbericText>&lt;!--DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd" --&gt;
   &lt;!-- Begin Block Tagged Note 9 - us-gaap:ScheduleOfVariableInterestEntitiesTextBlock--&gt;
   &lt;div style="margin-left: 0%"&gt;
   &lt;table width="100%" border="0" cellpadding="0" cellspacing="0" style="font-size: 10pt; font-family: Arial, Helvetica; color: #000000; background: transparent; text-align: left"&gt;
   &lt;tr&gt;
       &lt;td width="8%"&gt;&lt;/td&gt;
       &lt;td width="92%"&gt;&lt;/td&gt;
   &lt;/tr&gt;
   &lt;tr valign="top"&gt;
       &lt;td&gt;
       &lt;b&gt;&lt;font style="font-family: 'Times New Roman', Times"&gt;Note&amp;#160;9.&amp;#160;&amp;#160;&lt;/font&gt;&lt;/b&gt;
   &lt;/td&gt;
       &lt;td&gt;
       &lt;b&gt;&lt;font style="font-family: 'Times New Roman', Times"&gt;Variable
       Interest Entities&lt;/font&gt;&lt;/b&gt;
   &lt;/td&gt;
   &lt;/tr&gt;
   &lt;/table&gt;
   &lt;div style="margin-top: 6pt; font-size: 1pt"&gt;&amp;#160;
   &lt;/div&gt;
   &lt;div align="left" style="margin-left: 2%; margin-right: 0%; font-size: 10pt; font-family: Arial, Helvetica; color: #000000; background: #ffffff"&gt;
       &lt;b&gt;&lt;i&gt;&lt;font style="font-family: 'Times New Roman', Times"&gt;Troubled
       Debt Restructurings&lt;/font&gt;&lt;/i&gt;&lt;/b&gt;
   &lt;/div&gt;
   &lt;div style="margin-top: 6pt; font-size: 1pt"&gt;&amp;#160;
   &lt;/div&gt;
   &lt;div align="left" style="margin-left: 0%; margin-right: 0%; text-indent: 4%; font-size: 10pt; font-family: 'Times New Roman', Times; color: #000000; background: #ffffff"&gt;
       On January&amp;#160;1, 2010, we adopted new accounting guidance
       surrounding the consolidation of variable interest entities. The
       new guidance removes the exemption for troubled debt
       restructurings as events that may require the reconsideration of
       whether or not an entity is a variable interest entity. As a
       result, certain of our troubled debt restructurings, both those
       preceding and following the adoption date, were determined to
       qualify as events requiring the reconsideration of our borrowers
       as variable interest entities. Through reconsideration, we
       determined that certain of our borrowers involved in troubled
       debt restructurings did not hold sufficient equity at risk to
       finance their activities without subordinated financial support
       and, as a result, we have concluded that these borrowers were
       variable interest entities upon the adoption of the new guidance.
   &lt;/div&gt;
   &lt;div style="margin-top: 6pt; font-size: 1pt"&gt;&amp;#160;
   &lt;/div&gt;
   &lt;div align="left" style="margin-left: 0%; margin-right: 0%; text-indent: 4%; font-size: 10pt; font-family: 'Times New Roman', Times; color: #000000; background: #ffffff"&gt;
       However, we also determined that we should not consolidate these
       borrowers because we do not have a controlling financial
       interest. The equity investors of these borrowers have the power
       to direct the activities that will have the most significant
       impact on the economics of these borrowers. These equity
       investors&amp;#8217; interests also provide them with rights to
       receive benefits in the borrowers that could potentially be
       significant. As a result, we have determined that the equity
       investors continue to have a controlling financial interest in
       the borrowers subsequent to the restructuring.
   &lt;/div&gt;
   &lt;div style="margin-top: 6pt; font-size: 1pt"&gt;&amp;#160;
   &lt;/div&gt;
   &lt;div align="left" style="margin-left: 0%; margin-right: 0%; text-indent: 4%; font-size: 10pt; font-family: 'Times New Roman', Times; color: #000000; background: #ffffff"&gt;
       Our interests in borrowers qualifying as variable interest
       entities were approximately $347.1&amp;#160;million as of
       June&amp;#160;30, 2010 and are included in loans held for investment
       in our consolidated balance sheet. For certain of these
       borrowers, we may have obligations to fund additional amounts
       through either unfunded commitments or letters of credit issued
       to or on behalf of these borrowers. Consequently, our maximum
       exposure to loss as a result of our involvement with these
       entities was approximately $435.1&amp;#160;million as of
       June&amp;#160;30, 2010.
   &lt;/div&gt;
   &lt;div style="margin-top: 12pt; font-size: 1pt"&gt;&amp;#160;
   &lt;/div&gt;
   &lt;div align="left" style="margin-left: 2%; margin-right: 0%; font-size: 10pt; font-family: Arial, Helvetica; color: #000000; background: #ffffff"&gt;
       &lt;b&gt;&lt;i&gt;&lt;font style="font-family: 'Times New Roman', Times"&gt;Term
       Debt Securitizations&lt;/font&gt;&lt;/i&gt;&lt;/b&gt;
   &lt;/div&gt;
   &lt;div style="margin-top: 6pt; font-size: 1pt"&gt;&amp;#160;
   &lt;/div&gt;
   &lt;div align="left" style="margin-left: 0%; margin-right: 0%; text-indent: 4%; font-size: 10pt; font-family: 'Times New Roman', Times; color: #000000; background: #ffffff"&gt;
       In conjunction with our commercial term debt securitizations, we
       established and contributed loans to separate single purpose
       entities (collectively, referred to as the &amp;#8220;Issuers&amp;#8221;).
       The Issuers are structured to be legally isolated, bankruptcy
       remote entities. The Issuers issued notes and certificates that
       are collateralized by the underlying assets of the Issuers,
       primarily comprising contributed loans. We service the
       underlying loans contributed to the Issuers and earn periodic
       servicing fees paid from the cash flows of the underlying loans.
       We have no legal obligation to repay the outstanding notes or
       certificates or contribute additional assets to the entities. As
       of June&amp;#160;30, 2010 and December&amp;#160;31, 2009, the total
       outstanding balances of these commercial term debt
       securitizations were $3.0&amp;#160;billion and $3.7&amp;#160;billion,
       respectively. These amounts include approximately
       $1.0&amp;#160;billion of notes and certificates that we held as of
       June&amp;#160;30, 2010 and December&amp;#160;31, 2009.
   &lt;/div&gt;
   &lt;div style="margin-top: 6pt; font-size: 1pt"&gt;&amp;#160;
   &lt;/div&gt;
   &lt;div align="left" style="margin-left: 0%; margin-right: 0%; text-indent: 4%; font-size: 10pt; font-family: 'Times New Roman', Times; color: #000000; background: #ffffff"&gt;
       We have determined that the Issuers are variable interest
       entities, subject to applicable consolidation guidance. We have
       concluded that the entities were designed to pass along risks
       related to the credit performance of the underlying loan
       portfolio. Except as set forth below, as a result of our power
       to direct the activities that most significantly impact the
       credit performance of the underlying commercial loan portfolio
       and our economic interests in the Issuers, we have concluded
       that we are the primary beneficiary of each of the Issuers.
       Consequently, except as set forth below, we report the assets
       and liabilities of the Issuers in our consolidated financial
       statements, including the underlying loans and the issued notes
       and certificates held by third parties. As of June&amp;#160;30,
       2010&amp;#160;and December&amp;#160;31, 2009, the carrying amounts of
       the consolidated liabilities related to the Issuers and recorded
       in term debt in our consolidated balance sheets were
       $2.0&amp;#160;billion and $2.7&amp;#160;billion, respectively, and were
       related to obligations for which there is no recourse to us. As
       of June&amp;#160;30, 2010 and December&amp;#160;31, 2009, the carrying
       amounts of the consolidated assets related to the Issuers and
       recorded in loans held for investment, net in our consolidated
       balance sheets were $2.4&amp;#160;billion and $3.1&amp;#160;billion,
       respectively, which were related to assets that can only be used
       to settle obligations of the Issuers.
   &lt;/div&gt;
   &lt;!-- XBRL Pagebreak Begin --&gt;
   &lt;/div&gt;
   &lt;!-- END PAGE WIDTH --&gt;
   &lt;!-- PAGEBREAK --&gt;
   &lt;div style="margin-left: 0%"&gt;
   &lt;!-- BEGIN PAGE WIDTH --&gt;
   &lt;div align="center" style="margin-left: 0%; margin-right: 0%; font-size: 10pt; font-family: Arial, Helvetica; color: #000000; background: #ffffff"&gt;
   &lt;b&gt;
   &lt;font style="font-family: 'Times New Roman', Times"&gt;
   &lt;/font&gt;
   &lt;/b&gt;
   &lt;/div&gt;
   &lt;!-- XBRL Pagebreak End --&gt;
   &lt;div style="margin-top: 6pt; font-size: 1pt"&gt;&amp;#160;
   &lt;/div&gt;
   &lt;div align="left" style="margin-left: 0%; margin-right: 0%; text-indent: 4%; font-size: 10pt; font-family: 'Times New Roman', Times; color: #000000; background: #ffffff"&gt;
       In July 2010, we delegated certain of our collateral management
       and special servicing rights in one of the Issuers to a third
       party. This transaction is expected to result in the
       deconsolidation of this Issuer and the derecognition of loans
       held by the Issuer from our balance sheet. For additional
       information, see Note&amp;#160;20, &lt;i&gt;Subsequent Event&lt;/i&gt;.
   &lt;/div&gt;
   &lt;/div&gt;
</NonNumbericText>
          <NonNumericTextHeader>&lt;!--DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd" --&gt;
   &lt;!-- Begin Block Tagged Note</NonNumericTextHeader>
          <FootnoteIndexer />
          <hasSegments>false</hasSegments>
          <hasScenarios>false</hasScenarios>
          <DisplayDateInUSFormat>false</DisplayDateInUSFormat>
        </Cell>
      </Cells>
      <OriginalInstanceReportColumns />
      <ElementDataType>us-types:textBlockItemType</ElementDataType>
      <SimpleDataType>textblock</SimpleDataType>
      <ElementDefenition>Disclosure of variable interest entities (VIE), including, but not limited to the nature, purpose, size, and activities of the VIE, the carrying amount and classification of consolidated assets that are collateral for the VIE's obligations, lack of recourse if creditors (or beneficial interest holders) of a consolidated VIE have no recourse to the general credit of the primary beneficiary. An enterprise that holds a significant variable interest in a VIE but is not the primary beneficiary may disclose the nature of its involvement with the VIE and when that involvement began, the nature, purpose, size, and activities of the VIE and the enterprise's maximum exposure to loss as a result of its involvement with the VIE.</ElementDefenition>
      <ElementReferences>Reference 1: http://www.xbrl.org/2003/role/presentationRef
 -Publisher FASB
 -Name Statement of Financial Accounting Standard (FAS)
 -Number 140
 -Paragraph 35

Reference 2: http://www.xbrl.org/2003/role/presentationRef
 -Publisher FASB
 -Name FASB Interpretation (FIN)
 -Number 46R
 -Paragraph 2, 14, 15, 16, 23, 24, 25, 26

Reference 3: http://www.xbrl.org/2003/role/presentationRef
 -Publisher FASB
 -Name FASB Interpretation (FIN)
 -Number 46R
 -Paragraph 4
 -Subparagraph g

Reference 4: http://www.xbrl.org/2003/role/presentationRef
 -Publisher FASB
 -Name FASB Staff Position (FSP)
 -Number FAS140-4 and FIN46(R)-8
 -Paragraph C4
 -Subparagraph d

</ElementReferences>
      <IsTotalLabel>false</IsTotalLabel>
    </Row>
  </Rows>
  <Footnotes />
  <NumberOfCols>1</NumberOfCols>
  <NumberOfRows>2</NumberOfRows>
  <HasScenarios>false</HasScenarios>
  <MonetaryRoundingLevel>UnKnown</MonetaryRoundingLevel>
  <SharesRoundingLevel>UnKnown</SharesRoundingLevel>
  <PerShareRoundingLevel>UnKnown</PerShareRoundingLevel>
  <HasPureData>false</HasPureData>
  <SharesShouldBeRounded>true</SharesShouldBeRounded>
</InstanceReport>
