Mercosur faces a number of challenges in furthering its regional integration. This article considers whether theories developed for European regionalism, such as neo-functionalism and liberal inter-governmentalism, provide a suitable framework for analysing the Mercosur case. The article argues that economic and policy asymmetries as well as institutional, social and economic deficits hamper deepening regionalism. These asymmetries and deficits also jeopardise the further benefits that could arise from building on Mercosur's considerable achievements. Finally, the analysis warns against the dangers of politicisation of Mercosur and the importance of societal inclusion. It suggests that top-down state-led Mercosur regionalism could benefit from being turned upside-down by bottom-up societal interest in deeper integration in the current shifting international economic context. © 2013 Copyright Taylor and Francis Group, LLC.