Evaluation research is used to identify programs that achieve their intended outcomes. Researchers typically evaluate delinquency-prevention programs by using a quasi-experimental design that compares outcomes for the experimental treatment group with outcomes for some nonrandom comparison group, which is similar in characteristics to the experimental group. Different researchers often come to different conclusions about what does and does not work. More rigorous reviews use meta-analysis, a statistical method that combines results across studies in developing estimates of effects for alternative intervention strategies. Some “rating or certification systems” use expert panels or other screening processes in assessing the integrity of individual evaluations and defined criteria for “proven,” “promising,” or “exemplary” programs. Researchers have identified a dozen “proven” delinquency-prevention programs, and another 20 to 30 “promising” programs are still being tested. The most successful programs are those that prevent youth from engaging in delinquent behaviors in the first place. The article cites home-visiting programs that target pregnant teens and their at-risk infants and preschool education for at-risk children, including home visits or work with parents. Successful school-based programs can prevent drug use, delinquency, antisocial behavior, and early school drop-out. Community-based programs can divert first-time offenders from further encounters with the justice system. The most effective community programs emphasize family interactions and provide skills to adults who supervise and teach/train the child. A few States such as Florida, Pennsylvania, and Washington have begun to implement evidence-based programs. The challenge is to push these reforms into the mainstream of juvenile justice programming. 2 tables and 59 notes