In examining the effectiveness of offender treatment, this article attempts to integrate disparate bodies of knowledge. An overview of the effectiveness of offender treatment is presented. To put offender treatment into perspectives, the psychotherapy outcome literature for nonoffenders is briefly reviewed. The complexity of offender treatment is further explored by reviewing correlates and antecedents of criminality that include antisocial personality disorder, antisocial behavior in children, and substance abuse. Implications of the existing body of knowledge on future policy and more active involvement by psychologists are discussed.