The principles developed by Andrews and others represent the most coherent approach to treatment now available. Among these principles are that intervention efforts must be linked to criminogenic characteristics and that treatment providers should match client learning styles with staff teaching styles. Meta-analyses of adult and juvenile correctional interventions demonstrate that most correctional treatments for adult prisoners probably have modest positive efforts and that juvenile interventions are more effective than those designed for adults. Behavioral/cognitive treatments produce larger effects on average than do other treatments. Analyses of specific treatment domains indicate effective interventions. Cognitive skills training seems successful with adult probationers and specific subgroups of offenders. Intensive, in-prison drug treatment is effective, especially when combined with community aftercare. Education, vocational training, and prison labor programs have modest effects on reducing criminal recidivism and increase positive behavior in prison. Evidence on sex offender treatment interventions is less positive, probably because the target population is heterogeneous and treatments need to be tailored to specific offender deficits. Tables, appended methodological discussion, and 128 references (Author abstract modified)