The tax filing season is when the IRS has most of its contacts with taxpayers, answering questions and processing returns and refunds. The 2008 filing season was particularly challenging due to the unanticipated mandate to make economic stimulus payments. The filing season is also the start of IRS's efforts to ensure the newly filed returns are compliant with the tax laws. The auditor was asked to assess IRS's performance, describe the costs and foregone revenue of administering the economic stimulus payments, and identify any opportunities for improving filing season compliance checks. The auditor analyzed IRS performance data, reviewed IRS operations, and interviewed IRS officials. Includes recommendations. Charts and tables.