﻿<?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>Summary of Significant Accounting Policies</ReportName>
  <ReportLongName>0202 - Disclosure - Summary of Significant Accounting Policies</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>Summary of Significant Accounting Policies [Abstract]</Label>
      <Level>0</Level>
      <ElementName>id_SummaryOfSignificantAccountingPoliciesAbstract</ElementName>
      <ElementPrefix>id</ElementPrefix>
      <IsBaseElement>false</IsBaseElement>
      <BalanceType>na</BalanceType>
      <PeriodType>duration</PeriodType>
      <ShortDefinition>Summary of Significant Accounting Policies.</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>Summary of Significant Accounting Policies.</ElementDefenition>
      <IsTotalLabel>false</IsTotalLabel>
    </Row>
    <Row>
      <Id>3</Id>
      <Label>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES</Label>
      <Level>1</Level>
      <ElementName>us-gaap_SignificantAccountingPoliciesTextBlock</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 2 - us-gaap:SignificantAccountingPoliciesTextBlock--&gt;
   &lt;div style="font-family: 'Times New Roman',Times,serif"&gt;
   &lt;div align="left" style="font-size: 10pt; margin-top: 12pt"&gt;&lt;b&gt;2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES&lt;/b&gt;
   &lt;/div&gt;
   &lt;div align="left" style="font-size: 10pt; margin-top: 6pt; margin-left: 1%"&gt;&lt;i&gt;Basis of Presentation and Principles of Consolidation&lt;/i&gt;
   &lt;/div&gt;
   &lt;div align="left" style="font-size: 10pt; margin-top: 6pt"&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;The accompanying unaudited condensed consolidated financial statements reflect all
   adjustments, consisting only of normal recurring adjustments that in the opinion of management are
   necessary for a fair presentation of the financial statements for the interim periods. The
   unaudited condensed consolidated financial statements have been prepared in accordance with the
   regulations of the Securities and Exchange Commission (&amp;#8220;SEC&amp;#8221;) for interim financial statements, and
   in accordance with SEC rules, omit or condense certain information and footnote disclosures.
   Results for the interim periods are not necessarily indicative of results to be expected for any
   other interim period or for the full year. These financial statements should be read in conjunction
   with the consolidated financial statements and related notes included in the Company&amp;#8217;s Annual
   Report on Form 10-K filed on February&amp;#160;26, 2010. The consolidated financial statements include the
   accounts of L-1 and its wholly-owned subsidiaries, after elimination of material inter-company
   transactions and balances.
   &lt;/div&gt;
   &lt;div align="left" style="font-size: 10pt; margin-top: 6pt; margin-left: 1%"&gt;&lt;i&gt;Use of Estimates&lt;/i&gt;
   &lt;/div&gt;
   &lt;div align="left" style="font-size: 10pt; margin-top: 6pt"&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;The preparation of financial statements in conformity with accounting principles generally
   accepted in the United States of America requires management to make estimates and assumptions that
   affect the reported amounts of assets and liabilities and disclosure of contingent assets and
   liabilities at the date of the financial statements and the reported amounts of revenues and
   expenses during the reporting period. The most significant assumptions and estimates relate to the
   allocation of the purchase price of the acquired businesses, assessing the impairment of goodwill,
   other intangible assets and property and equipment, revenue recognition, estimating the useful life
   of long-lived assets, inventory valuation allowance, provision for bad debts, income taxes,
   litigation and valuation of and accounting for financial instruments, including convertible notes,
   interest rate protection agreements, foreign currency contracts, warrants and stock options. Actual
   results could differ materially from those estimates.
   &lt;/div&gt;
   &lt;div align="left" style="font-size: 10pt; margin-top: 6pt; margin-left: 1%"&gt;&lt;i&gt;Revenue Recognition&lt;/i&gt;
   &lt;/div&gt;
   &lt;div align="left" style="font-size: 10pt; margin-top: 6pt"&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;The Company derives its revenue from sales of solutions that include hardware components,
   consumables and software components and related maintenance, technical support, training and
   installation services integral to sales of hardware and software. The Company also derives revenues
   from sales of finger-print based background check enrollment services and government security and
   information technologies services. A customer, depending on its needs, may order solutions that
   include hardware, equipment, consumables, software products or services or combine these products
   and services to create a multiple element arrangement. The Company&amp;#8217;s revenue recognition policies
   are described in the notes to the consolidated financial statements included in the Company&amp;#8217;s
   Annual Report on Form 10-K filed on February&amp;#160;26, 2010. There have been no material changes to such
   policies.
   &lt;/div&gt;
   &lt;div align="left" style="font-size: 10pt; margin-top: 6pt; margin-left: 1%"&gt;&lt;i&gt;Stock-Based Compensation&lt;/i&gt;
   &lt;/div&gt;
   &lt;div align="left" style="font-size: 10pt; margin-top: 6pt"&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;L-1 uses the Black-Scholes valuation model to estimate the fair value of option awards. The
   following weighted average assumptions were utilized in the valuation of stock options in 2010 and
   2009:
   &lt;/div&gt;
   &lt;!-- Folio --&gt;
   &lt;!-- /Folio --&gt;
   &lt;/div&gt;
   &lt;!-- PAGEBREAK --&gt;
   &lt;div style="font-family: 'Times New Roman',Times,serif"&gt;
   &lt;div align="center"&gt;
   &lt;table style="font-size: 10pt; text-align: left" cellspacing="0" border="0" cellpadding="0" width="100%"&gt;
   &lt;!-- Begin Table Head --&gt;
   &lt;tr valign="bottom"&gt;
       &lt;td width="52%"&gt;&amp;#160;&lt;/td&gt;
       &lt;td width="5%"&gt;&amp;#160;&lt;/td&gt;
       &lt;td width="3%"&gt;&amp;#160;&lt;/td&gt;
       &lt;td width="1%"&gt;&amp;#160;&lt;/td&gt;
       &lt;td width="3%"&gt;&amp;#160;&lt;/td&gt;
       &lt;td width="5%"&gt;&amp;#160;&lt;/td&gt;
       &lt;td width="3%"&gt;&amp;#160;&lt;/td&gt;
       &lt;td width="1%"&gt;&amp;#160;&lt;/td&gt;
       &lt;td width="3%"&gt;&amp;#160;&lt;/td&gt;
       &lt;td width="5%"&gt;&amp;#160;&lt;/td&gt;
       &lt;td width="3%"&gt;&amp;#160;&lt;/td&gt;
       &lt;td width="1%"&gt;&amp;#160;&lt;/td&gt;
       &lt;td width="3%"&gt;&amp;#160;&lt;/td&gt;
       &lt;td width="5%"&gt;&amp;#160;&lt;/td&gt;
       &lt;td width="3%"&gt;&amp;#160;&lt;/td&gt;
       &lt;td width="1%"&gt;&amp;#160;&lt;/td&gt;
       &lt;td width="3%"&gt;&amp;#160;&lt;/td&gt;
   &lt;/tr&gt;
   &lt;tr style="font-size: 8pt" valign="bottom"&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td nowrap="nowrap" align="center" colspan="7" style="border-bottom: 1px solid #000000"&gt;&lt;b&gt;Three Months Ended&lt;/b&gt;&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td nowrap="nowrap" align="center" colspan="7" style="border-bottom: 1px solid #000000"&gt;&lt;b&gt;Six Months Ended&lt;/b&gt;&lt;/td&gt;
   &lt;/tr&gt;
   &lt;tr style="font-size: 8pt" valign="bottom"&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td nowrap="nowrap" align="center" colspan="3"&gt;&lt;b&gt;June 30,&lt;/b&gt;&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td nowrap="nowrap" align="center" colspan="3"&gt;&lt;b&gt;June 30,&lt;/b&gt;&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td nowrap="nowrap" align="center" colspan="3"&gt;&lt;b&gt;June 30,&lt;/b&gt;&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td nowrap="nowrap" align="center" colspan="3"&gt;&lt;b&gt;June 30,&lt;/b&gt;&lt;/td&gt;
   &lt;/tr&gt;
   &lt;tr style="font-size: 8pt" valign="bottom"&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td nowrap="nowrap" align="center" colspan="3" style="border-bottom: 1px solid #000000"&gt;&lt;b&gt;2010&lt;/b&gt;&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td nowrap="nowrap" align="center" colspan="3" style="border-bottom: 1px solid #000000"&gt;&lt;b&gt;2009&lt;/b&gt;&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td nowrap="nowrap" align="center" colspan="3" style="border-bottom: 1px solid #000000"&gt;&lt;b&gt;2010&lt;/b&gt;&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td nowrap="nowrap" align="center" colspan="3" style="border-bottom: 1px solid #000000"&gt;&lt;b&gt;2009&lt;/b&gt;&lt;/td&gt;
   &lt;/tr&gt;
   &lt;!-- End Table Head --&gt;
   &lt;!-- Begin Table Body --&gt;
   &lt;tr valign="bottom" style="background: #cceeff"&gt;
       &lt;td&gt;
   &lt;div style="margin-left:15px; text-indent:-15px"&gt;Expected common stock price volatility
   &lt;/div&gt;&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td nowrap="nowrap" align="right"&gt;&amp;#160;&lt;/td&gt;
       &lt;td align="right"&gt;55.4&lt;/td&gt;
       &lt;td nowrap="nowrap"&gt;%&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td nowrap="nowrap" align="right"&gt;&amp;#160;&lt;/td&gt;
       &lt;td align="right"&gt;58.4&lt;/td&gt;
       &lt;td nowrap="nowrap"&gt;%&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td nowrap="nowrap" align="right"&gt;&amp;#160;&lt;/td&gt;
       &lt;td align="right"&gt;56.4&lt;/td&gt;
       &lt;td nowrap="nowrap"&gt;%&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td nowrap="nowrap" align="right"&gt;&amp;#160;&lt;/td&gt;
       &lt;td align="right"&gt;57.8&lt;/td&gt;
       &lt;td nowrap="nowrap"&gt;%&lt;/td&gt;
   &lt;/tr&gt;
   &lt;tr valign="bottom"&gt;
       &lt;td&gt;
   &lt;div style="margin-left:15px; text-indent:-15px"&gt;Risk free interest rate
   &lt;/div&gt;&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td nowrap="nowrap" align="right"&gt;&amp;#160;&lt;/td&gt;
       &lt;td align="right"&gt;2.9&lt;/td&gt;
       &lt;td nowrap="nowrap"&gt;%&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td nowrap="nowrap" align="right"&gt;&amp;#160;&lt;/td&gt;
       &lt;td align="right"&gt;3.7&lt;/td&gt;
       &lt;td nowrap="nowrap"&gt;%&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td nowrap="nowrap" align="right"&gt;&amp;#160;&lt;/td&gt;
       &lt;td align="right"&gt;3.5&lt;/td&gt;
       &lt;td nowrap="nowrap"&gt;%&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td nowrap="nowrap" align="right"&gt;&amp;#160;&lt;/td&gt;
       &lt;td align="right"&gt;4.0&lt;/td&gt;
       &lt;td nowrap="nowrap"&gt;%&lt;/td&gt;
   &lt;/tr&gt;
   &lt;tr valign="bottom" style="background: #cceeff"&gt;
       &lt;td&gt;
   &lt;div style="margin-left:15px; text-indent:-15px"&gt;Expected life of options
   &lt;/div&gt;&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td colspan="3" nowrap="nowrap" align="center"&gt;6.3 Years&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td colspan="3" nowrap="nowrap" align="center"&gt;6.3 Years&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td colspan="3" nowrap="nowrap" align="center"&gt;6.3 Years&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td colspan="3" nowrap="nowrap" align="center"&gt;6.3 Years&lt;/td&gt;
   &lt;/tr&gt;
   &lt;tr valign="bottom"&gt;
       &lt;td&gt;
   &lt;div style="margin-left:15px; text-indent:-15px"&gt;Expected annual dividends
   &lt;/div&gt;&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td align="right"&gt;&amp;#8212;&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td align="right"&gt;&amp;#8212;&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td align="right"&gt;&amp;#8212;&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
       &lt;td align="right"&gt;&amp;#8212;&lt;/td&gt;
       &lt;td&gt;&amp;#160;&lt;/td&gt;
   &lt;/tr&gt;
   &lt;!-- End Table Body --&gt;
   &lt;/table&gt;
   &lt;/div&gt;
   &lt;div align="left" style="font-size: 10pt; margin-top: 6pt"&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;The expected volatility rate is based on the historical volatility of the Company&amp;#8217;s
   common stock. The expected life of options are calculated pursuant to the relevant guidance from
   Staff Accounting Bulletin No.&amp;#160;107. The Company estimates forfeitures based on historical rates. The
   risk free interest rate is based on the applicable treasury security whose term approximates the
   expected life of the options. The Company updates these assumptions on at least an annual basis and
   on an interim basis if significant changes to the assumptions are determined to be necessary.
   &lt;/div&gt;
   &lt;div align="left" style="font-size: 10pt; margin-top: 6pt; margin-left: 1%"&gt;&lt;i&gt;Computation of Net Loss per Share&lt;/i&gt;
   &lt;/div&gt;
   &lt;div align="left" style="font-size: 10pt; margin-top: 6pt"&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;Basic loss attributable to L-1&amp;#8217;s shareholders per share is calculated by dividing net loss
   attributable to L-1&amp;#8217;s shareholders by the weighted average number of common shares outstanding
   during the period. Diluted net loss attributable to L-1&amp;#8217;s shareholders per share is based upon the
   weighted average number of diluted shares outstanding during the period.
   &lt;/div&gt;
   &lt;div align="left" style="font-size: 10pt; margin-top: 6pt"&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;The weighted average number of shares of common stock outstanding during 2009, includes 1.1
   million shares issuable pursuant to the Series&amp;#160;A Convertible Preferred Stock before their
   conversion into common stock. Restricted share awards are included in the calculation of basic
   shares outstanding beginning on the date of vesting. The impact of approximately 0.2&amp;#160;million of
   common equivalent shares for the three and six month periods ended June&amp;#160;30, 2010 and the impact of
   0.1&amp;#160;million for the six month period ended June&amp;#160;30, 2009, were not reflected in the net loss
   attributable to L-1&amp;#8217;s shareholders per share as their effect would be anti-dilutive. There was no
   impact for the three month period ending June&amp;#160;30, 2009.
   &lt;/div&gt;
   &lt;div align="left" style="font-size: 10pt; margin-top: 6pt"&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;The Company calculates the effect of the Convertible Notes on diluted net loss attributable to
   L-1&amp;#8217;s shareholders per share utilizing the &amp;#8220;as if converted&amp;#8221; method since the Company has the right
   to issue shares of common stock to settle the entire obligation upon conversion. For the three and
   six month periods ended June&amp;#160;30, 2010 and 2009, the effect was anti-dilutive. Accordingly,
   approximately 5.5&amp;#160;million shares of weighted average common stock issuable at conversion have been
   excluded from the determination of weighted average diluted shares outstanding.
   &lt;/div&gt;
   &lt;div align="left" style="font-size: 10pt; margin-top: 6pt"&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;In connection with the issuance of the Convertible Notes, the Company entered into a pre-paid
   forward contract with Bear Stearns (now JP Morgan Chase) for a payment of $69.8&amp;#160;million to purchase
   3.5&amp;#160;million shares of the Company&amp;#8217;s common stock at a price of $20.00 per share for delivery in
   2012. The number of shares to be delivered under the contract is used to reduce weighted average
   basic and diluted shares outstanding for loss attributable to L-1&amp;#8217;s shareholders per share
   purposes.
   &lt;/div&gt;
   &lt;div align="left" style="font-size: 10pt; margin-top: 6pt; margin-left: 1%"&gt;&lt;i&gt;Adoption of New Accounting Standards&lt;/i&gt;
   &lt;/div&gt;
   &lt;div align="left" style="font-size: 10pt; margin-top: 6pt"&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;Effective January&amp;#160;1, 2010, the Company adopted the following accounting standards:
   &lt;/div&gt;
   &lt;div align="left" style="font-size: 10pt; margin-top: 6pt"&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;In June&amp;#160;2009, the FASB issued the standard, &lt;i&gt;&amp;#8220;Amendments to FASB Interpretation No.&amp;#160;46(R&lt;/i&gt;)&amp;#8221;. The
   standard changes the criteria to determine how an investee for a company is insufficiently
   capitalized or is not controlled through voting (or similar rights) and therefore should be
   consolidated. The adoption of this standard did not have a material impact on the financial
   statements for any of the periods presented.
   &lt;/div&gt;
   &lt;div align="left" style="font-size: 10pt; margin-top: 6pt"&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;In January&amp;#160;2010, the FASB issued the standard, &lt;i&gt;&amp;#8220;Fair Value Measurements and Disclosures &amp;#8212;
   Improving Disclosures about Fair Value Measurements&amp;#8221;. &lt;/i&gt;The adoption of this standard did not have a
   material impact on the financial statements for any of the periods presented.
   &lt;/div&gt;
   &lt;div align="left" style="font-size: 10pt; margin-top: 6pt; margin-left: 1%"&gt;&lt;i&gt;Recently Issued Accounting Standards&lt;/i&gt;
   &lt;/div&gt;
   &lt;div align="left" style="font-size: 10pt; margin-top: 6pt"&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;In October&amp;#160;2009, the FASB issued the standard, &lt;i&gt;&amp;#8220;Multiple Element Arrangements&amp;#8221;, &lt;/i&gt;which modifies
   accounting for multiple element arrangements by requiring that the separation of the arrangements
   be based on estimated selling prices based on entity specific assumptions rather than fair value,
   eliminating the residual method of allocation and requiring
   additional disclosures related to such
   arrangements. The standard is effective prospectively for arrangements entered into or materially
   modified in fiscal years beginning on or after June&amp;#160;15, 2010. The Company has not yet evaluated the
   impact the adoption of the standard will have on its consolidated financial statements.
   &lt;/div&gt;
   &lt;div align="left" style="font-size: 10pt; margin-top: 6pt"&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;Also in October&amp;#160;2009, the FASB issued the standard, &lt;i&gt;&amp;#8220;Certain Revenue Arrangements That Include
   Software Elements&amp;#8221;, &lt;/i&gt;which amends software revenue recognition guidance to eliminate from its scope
   tangible products containing software components that function together to deliver the tangible
   product&amp;#8217;s essential functionality and to provide guidance on how to allocate arrangement
   consideration to deliverables in an arrangement that contain both tangible products and software.
   The standard is effective prospectively for revenue arrangements entered into or materially
   modified in fiscal years beginning on or after June&amp;#160;15, 2010. The Company has not yet evaluated the
   impact the adoption of the standard will have on its consolidated financial statements.
   &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>This element may be used to describe all significant accounting policies of the reporting entity.</ElementDefenition>
      <ElementReferences>Reference 1: http://www.xbrl.org/2003/role/presentationRef
 -Publisher AICPA
 -Name Accounting Principles Board Opinion (APB)
 -Number 22
 -Paragraph 8

</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>
