<?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>104 - Disclosure - Accrued Expenses</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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&lt;div&gt;&lt;!--StartFragment--&gt; &lt;p style="BACKGROUND-COLOR: #ffffff; MARGIN-BOTTOM: 8px; MARGIN-TOP: 0px"&gt; Accrued expenses consist of the following:&lt;/p&gt; &lt;table style="FONT-SIZE: 10pt; MARGIN-TOP: 0px" cellspacing="0" cellpadding="0" width="100%"&gt; &lt;tr style="FONT-SIZE: 0px"&gt; &lt;td&gt;&amp;nbsp;&lt;/td&gt; &lt;td width="20"&gt;&amp;nbsp;&lt;/td&gt; &lt;td width="8"&gt;&amp;nbsp;&lt;/td&gt; &lt;td width="73"&gt;&amp;nbsp;&lt;/td&gt; &lt;td width="20"&gt;&amp;nbsp;&lt;/td&gt; &lt;td width="8"&gt;&amp;nbsp;&lt;/td&gt; &lt;td width="73"&gt;&amp;nbsp;&lt;/td&gt; &lt;td width="4"&gt;&amp;nbsp;&lt;/td&gt; &lt;/tr&gt; &lt;tr&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom"&gt; &lt;p style="FONT-SIZE: 8pt; MARGIN: 0px; text-align: center"&gt; &amp;nbsp;&lt;/p&gt; &lt;/td&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom" width="20"&gt; &lt;p style="FONT-SIZE: 8pt; PADDING-BOTTOM: 0px; PADDING-TOP: 0px; PADDING-LEFT: 0px; MARGIN: 0px; PADDING-RIGHT: 0px"&gt; &amp;nbsp;&lt;/p&gt; &lt;/td&gt; &lt;td style="BORDER-BOTTOM: #000000 1px solid; MARGIN-TOP: 0px" valign="bottom" width="81" colspan="2"&gt; &lt;p style="FONT-SIZE: 8pt; MARGIN: 0px; text-align: center"&gt; &lt;strong&gt;June&amp;nbsp;30,&lt;br /&gt; 2013&lt;/strong&gt;&lt;/p&gt; &lt;/td&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom" width="20"&gt; &lt;p style="FONT-SIZE: 8pt; PADDING-BOTTOM: 0px; PADDING-TOP: 0px; PADDING-LEFT: 0px; MARGIN: 0px; PADDING-RIGHT: 0px"&gt; &amp;nbsp;&lt;/p&gt; &lt;/td&gt; &lt;td style="BORDER-BOTTOM: #000000 1px solid; MARGIN-TOP: 0px" valign="bottom" width="81" colspan="2"&gt; &lt;p style="FONT-SIZE: 8pt; MARGIN: 0px; text-align: center"&gt; &lt;strong&gt;December&amp;nbsp;31,&lt;br /&gt; 2012&lt;/strong&gt;&lt;/p&gt; &lt;/td&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom" width="4"&gt; &lt;p style="FONT-SIZE: 8pt; PADDING-BOTTOM: 0px; PADDING-TOP: 0px; PADDING-LEFT: 0px; MARGIN: 0px; PADDING-RIGHT: 0px"&gt; &amp;nbsp;&lt;/p&gt; &lt;/td&gt; &lt;/tr&gt; &lt;tr&gt; &lt;td style="MARGIN-TOP: 0px; BACKGROUND-COLOR: #ccffcc" valign="bottom"&gt; &lt;p style="MARGIN: 0px"&gt;Compensation and related benefits&lt;/p&gt; &lt;/td&gt; &lt;td style="MARGIN-TOP: 0px; BACKGROUND-COLOR: #ccffcc" valign="bottom" width="20"&gt; &lt;p style="MARGIN: 0px"&gt;&amp;nbsp;&lt;/p&gt; &lt;/td&gt; &lt;td style="MARGIN-TOP: 0px; BACKGROUND-COLOR: #ccffcc" valign="bottom" width="8"&gt; &lt;p style="MARGIN: 0px"&gt;$&lt;/p&gt; &lt;/td&gt; &lt;td style="MARGIN-TOP: 0px; BACKGROUND-COLOR: #ccffcc" valign="bottom" width="73"&gt; &lt;p style="MARGIN: 0px; text-align: right"&gt;160,524&lt;/p&gt; &lt;/td&gt; &lt;td style="MARGIN-TOP: 0px; BACKGROUND-COLOR: #ccffcc" valign="bottom" width="20"&gt; &lt;p style="MARGIN: 0px"&gt;&amp;nbsp;&lt;/p&gt; &lt;/td&gt; &lt;td style="MARGIN-TOP: 0px; BACKGROUND-COLOR: #ccffcc" valign="bottom" width="8"&gt; &lt;p style="MARGIN: 0px"&gt;$&lt;/p&gt; &lt;/td&gt; &lt;td style="MARGIN-TOP: 0px; BACKGROUND-COLOR: #ccffcc" valign="bottom" width="73"&gt; &lt;p style="MARGIN: 0px; text-align: right"&gt;105,927&lt;/p&gt; &lt;/td&gt; &lt;td style="MARGIN-TOP: 0px; BACKGROUND-COLOR: #ccffcc" valign="bottom" width="4"&gt; &lt;p style="MARGIN: 0px"&gt;&amp;nbsp;&lt;/p&gt; &lt;/td&gt; &lt;/tr&gt; &lt;tr&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom"&gt; &lt;p style="MARGIN: 0px"&gt;Accrued patent fees&lt;/p&gt; &lt;/td&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom" width="20"&gt; &lt;p style="MARGIN: 0px"&gt;&amp;nbsp;&lt;/p&gt; &lt;/td&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom" width="8"&gt; &lt;p style="MARGIN: 0px"&gt;&amp;nbsp;&lt;/p&gt; &lt;/td&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom" width="73"&gt; &lt;p style="MARGIN: 0px; text-align: right"&gt;23,333&lt;/p&gt; &lt;/td&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom" width="20"&gt; &lt;p style="MARGIN: 0px"&gt;&amp;nbsp;&lt;/p&gt; &lt;/td&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom" width="8"&gt; &lt;p style="MARGIN: 0px"&gt;&amp;nbsp;&lt;/p&gt; &lt;/td&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom" width="73"&gt; &lt;p style="MARGIN: 0px; text-align: right"&gt;20,000&lt;/p&gt; &lt;/td&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom" width="4"&gt; &lt;p style="MARGIN: 0px"&gt;&amp;nbsp;&lt;/p&gt; &lt;/td&gt; &lt;/tr&gt; &lt;tr&gt; &lt;td style="MARGIN-TOP: 0px; BACKGROUND-COLOR: #ccffcc" valign="bottom"&gt; &lt;p style="MARGIN: 0px"&gt;Professional fees&lt;/p&gt; &lt;/td&gt; &lt;td style="MARGIN-TOP: 0px; BACKGROUND-COLOR: #ccffcc" valign="bottom" width="20"&gt; &lt;p style="MARGIN: 0px"&gt;&amp;nbsp;&lt;/p&gt; &lt;/td&gt; &lt;td style="BORDER-BOTTOM: #000000 1px solid; MARGIN-TOP: 0px; BACKGROUND-COLOR: #ccffcc" valign="bottom" width="8"&gt; &lt;p style="PADDING-BOTTOM: 0px; PADDING-TOP: 0px; PADDING-LEFT: 0px; MARGIN: 0px; PADDING-RIGHT: 0px"&gt; &amp;nbsp;&lt;/p&gt; &lt;/td&gt; &lt;td style="BORDER-BOTTOM: #000000 1px solid; MARGIN-TOP: 0px; BACKGROUND-COLOR: #ccffcc" valign="bottom" width="73"&gt; &lt;p style="MARGIN: 0px; text-align: right"&gt;27,781&lt;/p&gt; &lt;/td&gt; &lt;td style="BORDER-BOTTOM: #ffffff 1px solid; MARGIN-TOP: 0px; BACKGROUND-COLOR: #ccffcc" valign="bottom" width="20"&gt; &lt;p style="MARGIN: 0px"&gt;&amp;nbsp;&lt;/p&gt; &lt;/td&gt; &lt;td style="BORDER-BOTTOM: #000000 1px solid; MARGIN-TOP: 0px; BACKGROUND-COLOR: #ccffcc" valign="bottom" width="8"&gt; &lt;p style="PADDING-BOTTOM: 0px; PADDING-TOP: 0px; PADDING-LEFT: 0px; MARGIN: 0px; PADDING-RIGHT: 0px"&gt; &amp;nbsp;&lt;/p&gt; &lt;/td&gt; &lt;td style="BORDER-BOTTOM: #000000 1px solid; MARGIN-TOP: 0px; BACKGROUND-COLOR: #ccffcc" valign="bottom" width="73"&gt; &lt;p style="MARGIN: 0px; text-align: right"&gt;3,281&lt;/p&gt; &lt;/td&gt; &lt;td style="BORDER-BOTTOM: #ffffff 1px solid; MARGIN-TOP: 0px; BACKGROUND-COLOR: #ccffcc" valign="bottom" width="4"&gt; &lt;p style="MARGIN: 0px"&gt;&amp;nbsp;&lt;/p&gt; &lt;/td&gt; &lt;/tr&gt; &lt;tr&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom"&gt; &lt;p style="PADDING-BOTTOM: 0px; PADDING-TOP: 0px; PADDING-LEFT: 0px; MARGIN: 0px; PADDING-RIGHT: 0px"&gt; &amp;nbsp;&lt;/p&gt; &lt;/td&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom" width="20"&gt; &lt;p style="PADDING-BOTTOM: 0px; PADDING-TOP: 0px; PADDING-LEFT: 0px; MARGIN: 0px; PADDING-RIGHT: 0px"&gt; &amp;nbsp;&lt;/p&gt; &lt;/td&gt; &lt;td style="BORDER-BOTTOM: #000000 3px double; MARGIN-TOP: 0px" valign="bottom" width="8"&gt; &lt;p style="MARGIN: 0px"&gt;$&lt;/p&gt; &lt;/td&gt; &lt;td style="BORDER-BOTTOM: #000000 3px double; MARGIN-TOP: 0px" valign="bottom" width="73"&gt; &lt;p style="MARGIN: 0px; text-align: right"&gt;211,638&lt;/p&gt; &lt;/td&gt; &lt;td style="BORDER-BOTTOM: #ffffff 3px double; MARGIN-TOP: 0px" valign="bottom" width="20"&gt; &lt;p style="MARGIN: 0px"&gt;&amp;nbsp;&lt;/p&gt; &lt;/td&gt; &lt;td style="BORDER-BOTTOM: #000000 3px double; MARGIN-TOP: 0px" valign="bottom" width="8"&gt; &lt;p style="MARGIN: 0px"&gt;$&lt;/p&gt; &lt;/td&gt; &lt;td style="BORDER-BOTTOM: #000000 3px double; MARGIN-TOP: 0px" valign="bottom" width="73"&gt; &lt;p style="MARGIN: 0px; text-align: right"&gt;129,208&lt;/p&gt; &lt;/td&gt; &lt;td style="BORDER-BOTTOM: #ffffff 3px double; MARGIN-TOP: 0px" valign="bottom" width="4"&gt; 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