ABSTRACT Democratic theory asserts that the legitimacy of contemporary international and regional organisations rests on a degree of consensus expressed by various actors. The quest for diffuse support now extends beyond member states and explains the opening up of IOs/ROs to transnational civil society’s participation. Despite both notions being familiar to IR scholars, a more precise understanding is needed concerning the relationship between each concept, particularly with regard to the inclusion/exclusion nexus and in the still neglected study of organisations in the global South. Using a practice perspective, the paper offers a contribution to that understanding by proposing a micro-level analysis of the behavioural practices of both ROs and TCS using MERCOSUR and the OAS as case studies. A nalysis of the opening up of these organisations, and the concurrent engagement of civil society reveals how inclusion is still both incomplete and unequal. Political liberalisation of ROs thus remains an unfulfilled mandate.