Understanding the underpinnings of clinical depression is a complex task, which must include consideration of multiple factors. This chapter explores developmental variables, including family, individual and environmental, that might contribute to, or constitute, a predisposition to onset of depression during adolescence. It discusses family studies and intergenerational transmission; family warmth, support and cohesion; intergenerational transmission; and peer relationships and social competence. It reviews developmental processes that are central to the adolescent's formation of emotion regulation skills and sense of self. The chapter considers a working model of how developmental factors could contribute to lowering the threshold for depression. It considers how key elements of the child's and adolescent's developing personality contribute to increased risk for depression. The model that is presented further elaborates on factors leading to compromised attachment, incorporates the role of emotion regulation and focuses on a more holistic view of the development of depression.