This is a comprehensive meta-analysis of available research on the effects of intervention programs for adult offenders, which is based on 801 eligible controlled studies reported through 2014 identified by researchers. Variables describing the intervention, participating offender samples, research methods, and effects found on a range of outcome constructs were coded into a database for analysis. The major outcome categories examined were recidivism, substance use, employment, mental health, anger/hostility, and aggression/violence. Broad intervention approaches included those such as cognitive behavioral, structured group, counseling, and drug court programs.The meta-analysis seeks to examine outcomes of various types of interventions and identify the characteristics of programs and participants most closely associated with positive outcomes. It seeks to use the findings to construct and obtain feedback on effective practice guidelines within the adult correctional system.