<?xml version="1.0" encoding="us-ascii"?><InstanceReport xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"><Version>2.2.0.25</Version><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios><ReportLongName>0203 - Disclosure - Inventory</ReportLongName><DisplayLabelColumn>true</DisplayLabelColumn><ShowElementNames>false</ShowElementNames><RoundingOption /><HasEmbeddedReports>false</HasEmbeddedReports><Columns><Column><Id>1</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelColumn>false</LabelColumn><CurrencyCode>USD</CurrencyCode><FootnoteIndexer /><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios><MCU><KeyName>1/1/2010 - 12/31/2010
USD ($)

USD ($) / shares
</KeyName><CurrencySymbol>$</CurrencySymbol><contextRef><ContextID>Jan-01-2010_Dec-31-2010</ContextID><EntitySchema>http://www.sec.gov/CIK</EntitySchema><EntityValue>0001113481</EntityValue><PeriodDisplayName /><PeriodType>duration</PeriodType><PeriodStartDate>2010-01-01T00:00:00</PeriodStartDate><PeriodEndDate>2010-12-31T00:00:00</PeriodEndDate><Segments /><Scenarios /></contextRef><UPS><UnitProperty><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></UnitProperty><UnitProperty><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></UnitProperty><UnitProperty><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></UnitProperty></UPS><CurrencyCode>USD</CurrencyCode><OriginalCurrencyCode>USD</OriginalCurrencyCode></MCU><CurrencySymbol>$</CurrencySymbol><Labels><Label Id="1" Label="12 Months Ended" /><Label Id="2" Label="Dec. 31, 2010" /></Labels></Column></Columns><Rows><Row><Id>2</Id><IsAbstractGroupTitle>true</IsAbstractGroupTitle><Level>0</Level><ElementName>us-gaap_InventoryNetAbstract</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><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><PreferredLabelRole /><FootnoteIndexer /><Cells><Cell><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText /><NonNumericTextHeader /><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios></Cell></Cells><OriginalInstanceReportColumns /><Unit>Other</Unit><ElementDataType>xbrli:stringItemType</ElementDataType><SimpleDataType>string</SimpleDataType><ElementDefenition>No definition available.</ElementDefenition><IsTotalLabel>false</IsTotalLabel><IsEPS>false</IsEPS><Label>Inventory [Abstract]</Label></Row><Row><Id>3</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><Level>0</Level><ElementName>us-gaap_InventoryDisclosureTextBlock</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><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><PreferredLabelRole>verboselabel</PreferredLabelRole><FootnoteIndexer /><Cells><Cell><Id>1</Id><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 3 - us-gaap:InventoryDisclosureTextBlock--&gt;
   &lt;div style="margin-left: 0%"&gt;
   &lt;div style="margin-top: 12pt; font-size: 1pt"&gt;&amp;#160;
   &lt;/div&gt;
   &lt;table width="100%" border="0" cellpadding="0" cellspacing="0" style="font-size: 10pt; font-family: Arial, Helvetica; color: #0c1c47; background: transparent; text-align: left"&gt;
   &lt;tr&gt;
       &lt;td width="3%"&gt;&lt;/td&gt;
       &lt;td width="97%"&gt;&lt;/td&gt;
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   &lt;tr valign="top"&gt;
       &lt;td&gt;
       &lt;b&gt;&lt;font style="font-family: 'Times New Roman', Times"&gt;3.&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;Inventory&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: 0%; margin-right: 0%; text-indent: 4%; font-size: 10pt; font-family: 'Times New Roman', Times; color: #0c1c47; background: transparent"&gt;
       The major classes of inventory were as follows:
   &lt;/div&gt;
   &lt;div style="margin-top: 6pt; font-size: 1pt"&gt;&amp;#160;
   &lt;/div&gt;
   &lt;table border="0" width="100%" align="center" cellpadding="0" cellspacing="0" style="font-size: 10pt; font-family: 'Times New Roman', Times; color: #0c1c47; background: transparent; text-align: left"&gt;
   &lt;!-- Table Width Row BEGIN --&gt;
   &lt;tr style="font-size: 1pt" valign="bottom"&gt;
       &lt;td width="81%"&gt;&amp;#160;&lt;/td&gt;&lt;!-- colindex=01 type=maindata --&gt;
       &lt;td width="2%"&gt;&amp;#160;&lt;/td&gt;&lt;!-- colindex=02 type=gutter --&gt;
       &lt;td width="1%" align="right"&gt;&amp;#160;&lt;/td&gt;&lt;!-- colindex=02 type=lead --&gt;
       &lt;td width="5%" align="right"&gt;&amp;#160;&lt;/td&gt;&lt;!-- colindex=02 type=body --&gt;
       &lt;td width="1%" align="left"&gt;&amp;#160;&lt;/td&gt;&lt;!-- colindex=02 type=hang1 --&gt;
       &lt;td width="3%"&gt;&amp;#160;&lt;/td&gt;&lt;!-- colindex=03 type=gutter --&gt;
       &lt;td width="1%" align="right"&gt;&amp;#160;&lt;/td&gt;&lt;!-- colindex=03 type=lead --&gt;
       &lt;td width="5%" align="right"&gt;&amp;#160;&lt;/td&gt;&lt;!-- colindex=03 type=body --&gt;
       &lt;td width="1%" align="left"&gt;&amp;#160;&lt;/td&gt;&lt;!-- colindex=03 type=hang1 --&gt;
   &lt;/tr&gt;
   &lt;!-- Table Width Row END --&gt;
   &lt;!-- TableOutputHead --&gt;
   &lt;tr style="font-size: 8pt" valign="bottom" align="center"&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom" style="border-bottom: 1px solid #0c1c47"&gt;
       &lt;b&gt;&lt;font style="color: #0c1c47"&gt;Inventory&lt;/font&gt;&lt;/b&gt;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td colspan="2" nowrap="nowrap" align="center" valign="bottom" style="border-bottom: 1px solid #0c1c47"&gt;
       &lt;b&gt;&lt;font style="color: #0c1c47"&gt;2010&lt;/font&gt;&lt;/b&gt;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td colspan="2" nowrap="nowrap" align="center" valign="bottom" style="border-bottom: 1px solid #0c1c47"&gt;
       &lt;b&gt;&lt;font style="color: #0c1c47"&gt;2009&lt;/font&gt;&lt;/b&gt;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;/tr&gt;
   &lt;tr style="font-size: 8pt" valign="bottom" align="center"&gt;
   &lt;td nowrap="nowrap" align="center" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td colspan="6" align="center" valign="bottom"&gt;
       &lt;b&gt;&lt;font style="color: #0c1c47"&gt;(In thousands)&lt;/font&gt;&lt;/b&gt;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;/tr&gt;
   &lt;tr style="line-height: 3pt; font-size: 1pt"&gt;
   &lt;td&gt;&amp;#160;
   &lt;/td&gt;
   &lt;/tr&gt;
   &lt;!-- TableOutputBody --&gt;
   &lt;tr valign="bottom" style="background: #cceeff"&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &lt;div style="text-indent: -10pt; margin-left: 10pt"&gt;
       Raw materials
   &lt;/div&gt;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
       $
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="right" valign="bottom"&gt;
       9,801
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
       $
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="right" valign="bottom"&gt;
       13,609
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;/tr&gt;
   &lt;tr valign="bottom"&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &lt;div style="text-indent: -10pt; margin-left: 10pt"&gt;
       &lt;font style="white-space: nowrap"&gt;Work-in-progress&lt;/font&gt;
   &lt;/div&gt;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="right" valign="bottom"&gt;
       7,183
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="right" valign="bottom"&gt;
       8,646
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;/tr&gt;
   &lt;tr valign="bottom" style="background: #cceeff"&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &lt;div style="text-indent: -10pt; margin-left: 10pt"&gt;
       Finished goods
   &lt;/div&gt;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="right" valign="bottom"&gt;
       8,359
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="right" valign="bottom"&gt;
       3,581
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;/tr&gt;
   &lt;tr valign="bottom" style="font-size: 1pt"&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td style="border-top: 1px solid #0c1c47"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td style="border-top: 1px solid #0c1c47"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td style="border-top: 1px solid #0c1c47"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td style="border-top: 1px solid #0c1c47"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;/tr&gt;
   &lt;tr valign="bottom"&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &lt;div style="text-indent: -10pt; margin-left: 20pt"&gt;
       &lt;b&gt;Total&lt;/b&gt;
   &lt;/div&gt;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
       $
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="right" valign="bottom"&gt;
       25,343
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
       $
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="right" valign="bottom"&gt;
       25,836
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;/tr&gt;
   &lt;tr valign="bottom" style="font-size: 1pt"&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td style="border-top: 3px double #0c1c47"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td style="border-top: 3px double #0c1c47"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td style="border-top: 3px double #0c1c47"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td style="border-top: 3px double #0c1c47"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;/tr&gt;
   &lt;/table&gt;
   &lt;div align="left" style="margin-left: 0%; margin-right: 0%; text-indent: 0%; font-size: 10pt; font-family: 'Times New Roman', Times; color: #0c1c47; background: transparent"&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: #0c1c47; background: transparent"&gt;
       The Company reviews inventory, including inventory purchase
       commitments, for slow moving or obsolete amounts based on
       expected revenues. If annual revenues are less than expected,
       the Company may be required to make additional allowances for
       excess or obsolete inventory in the future.
   &lt;/div&gt;
   &lt;/div&gt;
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 -Publisher AICPA
 -Name Accounting Research Bulletin (ARB)
 -Number 43
 -Chapter 3
 -Section A
 -Paragraph 9

Reference 2: http://www.xbrl.org/2003/role/presentationRef
 -Publisher SEC
 -Name Regulation S-X (SX)
 -Number 210
 -Section 02
 -Paragraph 6
 -Subparagraph a, b, c
 -Article 5

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