Source: (2007) Criminal Justice and Behavior. 34(7): 879-892.The treatment literature on offender rehabilitation is reviewed with the purpose of deriving further direction for researchers and clinicians in the field of correctional psychology. After addressing the measurement of recidivism and other indicators of effectiveness, this empirically guided article reviews individual studies and meta-analyses on effectiveness of psychosocial correctional treatment for adult offenders and specialized treatment for substance abuse offenders and sexual offenders. A foundation in the general principles of offender intervention is established; principles such as risk, need, and responsivity are upheld; and common themes including the use of cognitive-behavioral interventions and the importance of treatment integrity emerge. However, questions move beyond “what works” to detailed queries about the nuances of effective service delivery, including client motivation. Well-controlled clinical studies and detailed process evaluations are still required. Other new directions include the application of positive psychology to offender treatment and the improvement of conditions under which community reentry is more likely to succeed. Directions for further research on correctional treatment are suggested.