The proposed project provides a historical analysis of the impact of human mobility on the institution of citizenship and the definition of citizenry in the countries that historically played a major role in founding the European Union. A useful cross-fertilization between history and the social sciences characterizes this innovative study of citizenship and nationhood in Western Europe, which compares the impact of migration on the policies and politics of citizenship of Belgium, France, (West) Germany, Ireland, Italy, the Netherlands, the United Kingdom, from the 19th century to the 1990s.This research brings an original contribution to the studies on citizenship in Europe and a deeper understanding of the political cultures and legal traditions underpinning them. It tackles questions that have been overlooked so far by studies of comparative political science, as it adopts a much-needed historical perspective to analyse each country's historical patterns of nationhood and legal traditions. It does not concentrate only on immigration, but it assesses as well the influences of both emigration and internal migration on their politics and policies of citizenship.The project represents an important attempt to bridge history and socials sciences in their study of citizenship and the definition of citizenry. It turns to theory to explain historical data and analyses on the relationship between migration and citizenship, in an attempt both to overcome the disciplinary tendency of historians to build narratives of the particular and to avoid any methodological nationalism. At the same time, it offers a major contribution to the development of theories on citizenship by challenging them against the litmus tests of history and broad comparison.