Guided by an ecological framework, we explore how siblings' and parents' roles, relationships, and activities are intertwined in everyday life, providing unique and combined contributions to development. In a departure from past research that emphasized the separate contributions of siblings and parents to individual development, we find that examining the conjoint or interactive effects of sibling and parent influences promises to extend our understanding of the role of family in children's and adolescents' social, emotional, and cognitive development. Understood within the context of family and sociocultural characteristics, siblings' unique roles as agents of socialization are illuminated.