What does it take to become a citizen of a particular nation? In a globalizing world, and with increasing international mobility, is it justified to restrict membership of a society? If so, on what grounds? Do societies need a distinctive national culture in order to thrive -- and should this be a factor in the allocation of citizenship to those migrating from elsewhere? How is national identity actually perceived among the existing citizens of western countries? In this volume major commentators, from a range of critical perspectives, explore a series of pressing, controversial issues surrounding the acquisition of citizenship, in theory and practice. These issues are of key importance for policy makers and social institutions, and for the self-understanding of contemporary societies. This book will be vital reading for students and researchers in Political Theory, Sociology, Law, Social Policy, Ethics, and other disciplines where the current debates around migration and citizenship apply.