This chapter examines the origins of physical aggression and violence from a developmental perspective. It focuses on how anger regulation and social contingencies in parent-child and peer interaction contribute to early development of aggression, and how individual differences in children's attention deployment and impulsivity moderate these social processes. From a social learning perspective, socialization occurs in the cumulative, day-to-day interactions of children with their parents, siblings, peers, and teachers. Social learning theory relies heavily on observable social interaction in family and peer settings to ascertain the proximal social processes that evoke, shape, maintain, and elaborate aggressive behavior. Gender differences in physical aggression have multiple determinants. Parents and peers play important but complementary roles in socialization. Early interventions that alter group contingencies for physical aggression and disruptive behavior hold particular promise. These programs can be applied in hallways, lunchrooms, and play-grounds where adult monitoring and contingencies are often nonsystematic and minimal.