GAO's work over the past several years has demonstrated that improper payments are a long-standing, widespread, and significant problem in the federal government. The Improper Payments Information Act of 2002 (IPIA) has increased visibility over improper payments by requiring executive branch agency heads, using guidance from the Office of Management and Budget, to identify programs and activities susceptible to significant improper payments, estimate amounts improperly paid, and report on the amounts of improper payments and their actions to reduce them. This testimony addresses (1) progress made in agencies' implementation of IPIA for fiscal year 2008, and (2) several major challenges that continue to hinder full reporting of IPIA information. GAO was also asked to provide an overview of Medicare and Medicaid programs' implementation of IPIA. This testimony is based primarily on GAO products, Office of Inspector General (OIG) audit reports, and agencies' fiscal year 2008 reported improper payment information, including information reported by the Department of Health and Human Service's (HHS) Centers for Medicare and Medicaid Services (CMS). GAO also analyzed fiscal year 2008 governmentwide improper payment information to identify trends and reviewed Medicare and Medicaid programs' reported actions to identify, estimate, and reduce improper payments.