The chapter attempts to determine whether intervention programs generally are capable of reducing reoffending rates for serious delinquents and, if so, what types of programs are most effective. The review reported in this chapter used techniques of meta-analysis to synthesize experimental and quasi-experimental research on the effectiveness of intervention for serious juvenile offenders. The review examined programs for offenders in the community, though possibly on probation or parole, and programs for institutionalized juvenile offenders. The average intervention effect for these studies was positive, statistically significant, and equivalent to a recidivism reduction of about 6 percentage points, for example, from 50 percent to 44 percent (mean effect size =.12). The variation around this overall mean, however, was considerable. With regard to the effectiveness of interventions, the chapter notes that it depends on a good match between program concept, host organization, and the clientele targeted. Tables, appendix, bibliography