Citizenship was the hallmark of political belonging in Europe during the 20th century. It determined a person's protection and freedom, and thus their chances of life and survival. For the first time, this book tells a shared history of citizenship in Western and Eastern Europe, from the peak of the nation-state to the present day, which is shaped by the crises of the European Union. It is the story of a central legal institution that significantly represents and simultaneously determines struggles over migration, integration, and belonging. One of the themes of this book is what lessons can be drawn from this history regarding the future prospects of European citizenship.