Although we live in a period of unprecedented globalization and mass migration, many contemporary western liberal democracies are asserting their sovereignty over who gets to become members of their polities with renewed ferocity. Citizenship matters more than ever. In this book, Elizabeth F. Cohen and Cyril Ghosh provide a concise and comprehensive introduction to the concept of citizenship and evaluate the idea's continuing relevance in the 21st century. They examine multiple facets of the concept, including the classic and contemporary theories that inform the practice of citizenship, the historical development of citizenship as a practice, and citizenship as an instrument of administrative rationality as well as lived experience. They show how access to a range of rights and privileges that accrue from citizenship in countries of the global north is creating a global citizenship-based caste system. This skillful critical appraisal of citizenship in the context of phenomena such as the global refugee crisis, South-North migration, and growing demands for minority rights will be essential reading for students and scholars of citizenship, migration studies and democratic theory.