In this book, Peter J. Spiro expands on his earlier works with a tour de force of modern citizenship practices, their normative evaluation, and the repercussions at the international level. The meticulously researched monograph offers a well-written account of the development of declarations, decisions, and practices over time to allow or disavow dual citizenship. The book complements other recent volumes showing that countries increasingly embrace multiple citizenship, such as Thomas Faist and Peter Kivisto’s Dual Citizenship in Global Perspective: From Unitary to Multiple Citizenship and David Cook-Martin’s The Scramble for Citizens: Dual Nationality and State Competition for Immigrants. It also highlights the need to understand the link between dual state membership, individual identification processes, and economic or political behavior.

Going beyond legislative and administrative practices, Spiro also looks at the role of public international law, domestic courts, official narratives, public discourses, and the politics of citizenship, which ultimately define the law on the books as much as the law in action. He showcases the difficulties of transposing sociological concepts, such as “divided loyalty,” onto legally enforceable categories, for example, stripping citizens of their citizenship when they move back to t