The social dimension of membership offers a strategic entry point for analyzing the development of citizenship in the European Union (EU). The first part of this contribution discusses the functions of social citizenship in this emerging supra-national and multi-level governance network. Second, the analysis deals with two prominent and stylized paradigms that have sought to make sense of the multi-level quality of social citizenship in the EU: residual, and post-national concepts of membership and citizenship in liberal democracies. Although each of these approaches captures selected elements of social citizenship, they are unable to deal in a satisfactory way with rights on duties on multiple governance levels. Therefore, the discussion moves to an alternative concept, namely nested citizenship. This means that regional, national and supra-national forms of citizenship function in complementary ways, while the associated norms, rules and instutions are under constant revision and further development. Third, the analysis shows that the concept of nested citizenship can help to overcome the fruitless dichotomy of Euro-optimism and Euro-pessimism concerning social policy and social citizenship. Both ideal-tpyical positions extrapolate the conditions of the nation-state to the supra-national level. Instead, this discussion suggests to conceive of European social citizenship as a ‘projet’ (Sartre), evolving towards a common past, present and future understanding of democratic principles and substantial rights