In this paper, the findings are described of Project STARS sub-project 2, in which a multi-method approach (longitudinal questionnaires, observations, meta-analysis) was used to investigate how different aspects of adolescents’ developing sexuality (behaviors, cognitions, emotions) are related over time to various aspects of adolescents’ relations with parents and peers. The results showed that adolescents who had a better relationship with their parents had less intention to have sex, began having sex at a later age, and also experienced more positive emotions after sex through a higher self-esteem. Although adolescents who frequently talked with their parents about sex were more sexually active later on, the frequency of sexual communication did not affect the sexual intentions of sexually inexperienced adolescents. Adolescents who interacted with peers more frequently, who thought that their friends were more sexually active and that they approved more of having sex, and who experienced more peer pressure to have sex, were also more sexually active themselves, and at an earlier age. Moreover, youth who had more deviant conversations about sex with their friends believed that their peers approved more of having sex, that they were more sexually active and that they had more risky sex. When parents and peers were examined simultaneously, only peers were found to play a role in adolescents’ timing of sexual debut. Frequent communication about sex with parents, however, buffered the effects of sexual peer norms on adolescents’ own sexual intentions. Theoretical and practical implications are discussed.