In this chapter, we provide an overview of our studies that have explored the relations between Indonesian Muslim adolescents’ religiosity and spirituality with their social competence and their relationships with peers and parents. We first reviewed our findings that individual differences in adolescent religiosity and spirituality (SR) was associated with multiple aspects of competence including positive associations with peer acceptance, prosocial behavior, regulation, self-esteem, and academic achievement and negative associations with externalizing behavior, loneliness, and aggression. We then reviewed studies suggesting that religious adolescents tended to develop friendships with others of similar religiosity. These associations predicted that adolescents who were friends with highly religious peers increased their religiosity over time. Finally, we looked at the interconnection between parent–adolescent relations and adolescent SR and adjustment. Parental warmth moderated the relation between parent religiosity and adolescent SR, and SR mediated the relation between parental warmth, parental religiosity, and adolescent prosocial behavior. These results are consistent with our view that in this highly religious community, religion is strongly associated with multiple aspects of adolescents’ lives. Second, we argue that adolescent religiosity must necessarily be understood within a relationship context, an idea that is consistent with an ecological perspective on child and adolescent religiousness.