The chapter contends that a considerable proportion of the disruptiveness, overt aggression and other interpersonal difficulties which occur in schools, detention centers, residential treatment facilities, and community and related settings reflect prosocial skill deficiencies. A substantial body of research supports this view of prosocial skill deficiency as an antecedent and correlate of antisocial behavior. Aggression Replacement Training (A.R.T.) is a multimodal, psychoeducational intervention with three components, each of which an aggressive youngster attends on a weekly basis: (1) Skillstreaming, a 50-skill curriculum of prosocial behaviors; (2) Anger Control Training; and (3) Moral Education, a set of procedures to raise the young person's level of fairness, justice, and concern with the needs and rights of others. The chapter reports on studies of the efficacy of A.R.T. at several youth centers. The chapter concludes that A.R.T. is effective. It appears to promote skills acquisition and performance, improves anger control, decreases the frequency of acting-out behavior, and increases the frequency of constructive, prosocial behaviors. Effects persist beyond institutional walls. The chapter includes discussion questions based on the information presented. Tables, references