The centrality of boundaries to the adolescent experience is reviewed from a variety of perspectives, such as the development and consolidation of the self, superego internalization and authority, and the encounter between self and other. The study of boundaries through the experiential modes of Being and Doing leads to distinguishing two kinds of boundary experiences, one requiring separation and differentiation, the other leading to merger and fusion. Adolescence entails the integration of these two modalities so that identity formation and intimacy can take place. The implications for treatment are discussed and illustrated with a clinical vignette.