This paper examines the formal features, the political rationale, distinctiveness, potential, and difficulties of post-liberal regionalism, with a particular focus on the case of UNASUR. Through this organization, traditional unionism and aspirations of Latin American regional integration are redefined in a South American geographic and ideational framework. Through this strategy South America became a political and economic construct in order to respond to globalization challenges and to achieve its members’ goals in development, regional autonomy (particularly in regards to the US), international influence and at the same time domestic governance of the involved countries. Nevertheless, the limits of this project’s future are being defined by nationalism, traditional visions of sovereignty and by a regional construction that involve significant institutional limitations, which are product of its intergovernmental logic, internal asymmetries and ambivalent Brazilian leadership