In drawing on several recent efforts to analyze evidence of what works in delinquency prevention, this study relied on the Washington State Institute of Public Policy's cost-benefit analysis of a number of juvenile delinquency prevention and intervention programs. The Federal Office of Juvenile Justice and Delinquency Prevention's Model Programs Guide also informed this study, in addition to several programs and strategies developed in Wisconsin. In the area of primary prevention, the study focused on preschool education, family support programs, and social-emotional learning programs. Secondary-prevention programs analyzed were family training programs, social skills training programs, mentoring programs, and vocational/job training programs. The types of juvenile offender programs examined were diversion or community accountability programs, therapeutic interventions, and case management/multimodal interventions. Within each program category, this report highlights a few evidence-based programs, including cost-benefit information where available. Practices and approaches that apparently increase program effectiveness within each category are also discussed. The report indicates that the most cost-effective prevention programs reviewed included preschool education, home visitation programs, and social and emotional learning programs for elementary school children. Among juvenile offender programs, the strongest empirical evidence of cost-effectiveness is for diversion programs and therapeutic interventions that provide a range of intensive services over relatively long time periods. Recommendations are offered for consideration by the Wisconsin Governor's Juvenile Justice Commission. 1 table, 108 references, and appended evidence-based program details, a list of program registries, and guidelines for selecting evidence-based programs