This article aims to address a fundamental question for analysts and students of MERCOSUR: what explains the bloc's survival despite its recurrent crises and frequent pessimistic forecasts predicting its collapse? It argues that the maintenance of co-operation after 1999, when the economic and political economy rationale of the project had almost disappeared, is best understood in terms of the convergent strategic interests of MERCOSUR partners. This convergence of interests in the continuity of the regional regime reflects three types of strategic incentives. First, defensive considerations reflecting external forces and a shared sense of vulnerability vis-à-vis the external environment have provided the main motivation for partners to engage in negotiations and attempt to move the process of integration forward. Secondly, the offensive incentives faced by Brazil, given its relatively stronger position within the region have also worked to foster regional co-operation. But besides these power considerations, the sustainability of co-operation has been at least partially assisted by an emerging process of socialisation among executive officials taking place within regional institutions. These processes of increased interaction and enmeshment have reinforced interests in regional integration, giving way to positive incentives to maintain MERCOSUR.