This study examined the relationship between perceived socialization from parents, school, peers, and media and adolescents' cognitive susceptibility to initiating sexual intercourse and transition to intercourse 2 years later. Baseline and follow-up in-home Audio-Computer Assisted Self Interview surveys were completed by 854 Black and White male and female adolescents who, at baseline, were 12–14 years old and had not engaged in sexual intercourse. Results showed that stronger connections to parents and schools and less exposure to permissive sexual norms from peers and media were associated with less susceptibility and sexual behavior, especially among White adolescents. Susceptibility mediated 38–64% of the relations between parent and school socialization and sexual intercourse behavior, and mediated 28–53% of the peer and media socialization links to behavior. Findings provide support for social cognitive models of adolescents' behavior and suggest potential strategies for successful interventions to delay initiation of sexual intercourse.