Because social competency is an important element for adolescents' healthy development, a central question is what can be done to help adolescents achieve and maintain social competency. This report details antecedents of two key aspects of social competency: quality social relationships and good social skills. For each social relationship and social skill, research evidence is presented from individual-, family-, peer-, and community-level factors shown to relate to the development of quality social relationships or good social skills. Intervention programs demonstrating improvements in adolescents' social relationships or skills are also described. Social relationships considered are in the family domain (parents, siblings, grandparents, other family members) and non-family domain (peers, other adults). Social skills described are interpersonal (conflict resolution, intimacy, prosocial behaviors) and individual attributes (self-control, social confidence, and empathy/sympathy). The emphasis is on evaluation studies implementing rigorous experimental designs and longitudinal studies examining predictors of social relationships/skills using multivariate analyses. The report restricts attention to studies assessing outcomes during adolescence. The report concludes by noting that important antecedents to quality social relationships include a positive parent-child relationship, parenting style, low family discord/parental divorce, and proximity to non-familial adults and peers. Antecedents of good social skills include individual characteristics of warmth and friendliness, nonverbal intelligence, responsive parenting, and sibling availability. Few experimentally-evaluated programs have attempted to increase relationship quality but several have attempted to increase social skills. The paper identifies future research directions. (Contains 324 references.) (KB)