Social competence, e.g., effective functioning in interpersonal relationships, plays an important role in well being during one's lifetime. Social skills, such as perspective taking and understanding intentionality, develop during childhood and adolescence. We hypothesize that these behavioral changes result from protracted development of brain regions involved in social interactions. We give a brief outline of behavioral and neuroimaging studies on fairness, trust, and reciprocity considerations in social decision making and the development of these considerations. We propose that a better understanding of the mechanisms underlying the developing brain and sociocognitive skills is important for understanding the development of social relationships.