Social relationships promote health and wellbeing. Brain regions regulating social behavior continue to develop throughout adolescence, as teens learn to navigate their social environment with increasing sophistication. Adolescence is also a time of increased risk for the development of psychiatric disorders, many of which are characteristically associated with social dysfunction. In this review, we consider the links between adolescent brain development and the broader social environment. We examine evidence that individual differences in social ability, partly determined by genetic influences on brain structure and function, impact the quality and quantity of social ties during adolescence and that, conversely, the structure of one's social network exerts complex yet profound influences on individual behavior and mental health. In this way, the brain and social environment sculpt each other throughout the teenage years to influence one's social standing amongst peers. Reciprocal interactions between brain maturation and the social environment at this critical developmental stage may augment risk or promote resilience for mental illness and other health outcomes.