A term of antique provenance, ‘cosmopolitanism’ has developed and cohered into a critical concept in contemporary social and cultural analysis. However, the daunting quantity (and variable quality) of the available research exploring the many, often controversial, issues attendant upon cosmopolitanism–and the breadth and complexity of the canon on which it draws–makes it difficult to discriminate the useful from the tendentious, superficial, and otiose. That is why this new title in the highly regarded Routledge series, Critical Concepts in Sociology, is so timely. It answers the urgent need for a wide-ranging collection to provide easy access to the key items of scholarly literature, material that is often inaccessible or scattered throughout a variety of specialist journals and books. In four volumes, this new collection addresses how key issues, such as globalization, migration, citizenship, social belonging, and cultural complexity and blending, are illuminated by reflections upon what cosmopolitanism is, or could be; and how cosmopolitan thinking and practice could, or does, impact upon such matters. The gathered materials also make sense of the revolutionary effects that debates on cosmopolitanism are having on research agendas and ways of thinking in sociology, and across the social sciences and humanities more generally. Cosmopolitanism is supplemented with a full index, and includes a comprehensive introduction, newly written by the editors, which places the collected material in its historical and intellectual context. It is destined to be valued by scholars, students, and researchers as a vital research resource.