During fiscal year 2002, Medicaid--a program jointly funded by the federal government and the states--provided health care coverage for about 51 million low-income Americans. That year, Medicaid benefit payments reached approximately $244 billion, of which the federal share was about $139 billion. The program is administered by state Medicaid agencies with oversight provided by the Centers for Medicare & Medicaid Services (CMS) in the Department of Health and Human Services. Medicaid's size and diversity make it vulnerable to improper payments that can result from fraud, abuse, or clerical errors. States conduct program integrity activities to prevent, or detect and recover, improper payments. This report provides information on (1) the types of provider fraud and abuse problems that state Medicaid programs have identified, (2) approaches states take to ensure that Medicaid funds are paid appropriately, and (3) CMS's efforts to support and oversee state program integrity activities. To address these issues, we compiled an inventory of states' Medicaid program integrity activities, conducted site visits in eight states, and interviewed CMS's Medicaid program integrity staff.