Book excerpt: This book introduces the concept of 'act of citizenship' and in doing so, re-orients the study of what it means to be a citizen. Isin and Nielsen show that an 'act of citizenship' is the event through which subjects constitute themselves as citizens. They claim that such an act involves both responsibility and answerability, but is ultimately irreducible to either. This study of citizenship is truly interdisciplinary, drawing not only on new developments in politics, sociology, geography and anthropology, but also on psychoanalysis, philosophy and history. Ranging from Antigone and Socrates in the ancient world to checkpoints, euthanasia and flash mobs in the modern one, the 'acts' and chapters here build up a dynamic and wide-ranging picture. Acts of Citizenship provides important new insights for all those concerned with the relationship between individuals, groups and polities.