Regional cooperation in social policy has gained momentum in Latin America. With the onset of the twenty first century, regional initiatives moved beyond traditional goals of trade and market liberalization, and new arrangements and practices were established in fields such as education, health, and employment. These initiatives, however, have not altered the traditional pattern of Latin American regionalism and decision-making remains highly intergovernmental. The question that comes next then is how and why cooperation has been pursued in these new and more contested policy areas. In search for an answer to this puzzle, this paper looks into the actors, institutions and processes underlying regional organizations’ involvement in social policies. More specifically, it explores the role of policy networks bringing state and societal actors and involving both formal institutions and informal linkages. Based on the analysis of health and higher education policy dynamics in MERCOSUR, the paper aims to unravel how and to what extent regional policy networks have worked as a site for the diffusion of policy ideas and expertise, thus promoting this bloc’s regulatory expansion into social policy. Moreover, a lingering question is whether and how these networks can sustain and further develop such policy areas in a regional and international context marked by uncertainty.