The deepening of European integration has altered the institutional configuration of social rights by weakening the traditional coercive monopoly of the state on actors and resources which are crucial for domestic redistributive arrangements. The article investigates such process in four steps. Firstly, it revisits the classical notion of citizenship - stressing the importance of "boundaries" - in order to offer both an adequate conceptualisation and a historical background to the problem. Secondly, it focuses on social rights proper and develops an argument about the way in which European integration is re-defining and challenging the established boundaries of social citizenship, in its national configuration. Thirdly, it offers a detailed map of how social rights actually operate in the EU, at different levels of provision. The map is organised around two dimensions: a territorial dimension, highlighting new exit/entry options across geographical frontiers and a membership dimension, highlighting the different degree of closure of the various "pillars" of social protection. The final paragraph discusses emerging trends and future options for post-national forms of social protection.