This report is based on a literature review and six site visits to the California Auditor General, the San Diego County Auditor Controller; the South Carolina Department of Social Services, Division of Investigations; and the Texas Department of Social Services, Division of Investigation. The monograph describes the conditions that permit fraud and abuse and presents practical prevention approaches. Discussion of the roles of program design and information systems in these programs includes analysis of design flaws and methods to overcome them. Special-purpose fraud prevention techniques are identified, including investigation, quality control, and corrective action units; the inspector general; peer review units; vulnerability assessment using live testing; hotlines; and fraud alert bulletins and newsletters. Routine prevention activities include periodic audits, investigative training, verification of information from service providers and clients, and public education efforts. It is recommended that any comprehensive fraud prevention program include both audit and investigation components, as well as budget, prosecution, management improvement, and public information sections. Program staff require skills in training, analysis, policy review, information sharing, and implementation. The fraud prevention strategy should not require major additions to the workforce. It should minimize incentives and opportunities for fraud and abuse, such as increasing the possibility of discovery, saving more than it costs, and including remedies for defects in program design. A successful strategy should also include safeguards for clients and providers and ways of mobilizing public support. Chapter references, tables, footnotes, an interview guide, and a bibliography listing 44 references are supplied.