We live in a rapidly changing world. The collapse of the Cold War, the development of new technologies and the globalisation of the world economy have all had a dramatic impact on societies across the globe. Migration, new types of wars and changing borders mean that even the stability and security of nation-states has become a thing of the past. New nationalisms, new social movements and the resurgence of identity politics all indicate that we are entering a new era where the very notion of collective identity -- through nation states or through transnational identity culture -- is challenged. This volume examines concepts of collective identity, how they are changing and what this means for our future. With contributions from distinguished sociologists including Jenkins, Eisenstadt, Rex, Bauman and Hall, it gives a radical new overview of collectivity theory -- a topic that lies at the heart of sociology, anthropology and political science.