This project aims to investigate the developments of the social dimension of European citizenship since the 1960s through the lenses of political science and history. The empirical focus will lie with the granting of transnational social rights related to social security (understood as a protection against social risks related to work, unemployment, healthcare, pensions, and poverty) to individuals. The main hypothesis guiding the research is posits a non-linear trajectory in the building of a European social citizenship. A progressive enlargement of rights occurred from an original focus on the Common Market in the 1960s to an embryonic social citizenship in the 2000s, followed by a new shrinking of rights onto a new kind of market citizenship catalysed by the latest recession and its political consequences over the last decade. The research team will make a contribution to existing research in three respects by: 1. Documenting the movement of construction and deconstruction of European social rights over time; 2. Substantiating the conceptual and empirical distinction between market and social citizenship; 3. Documenting the resulting social stratification between categories of people enjoying more or less rights (national citizens, non-national EU citizens, non-EU citizens).