Book excerpt: Immigration has transformed the social, economic, political and cultural landscapes of global cities such as London, Melbourne, Milan and Amsterdam. The term ‘superdiversity’ captures a new era of migration-driven demographic diversifications and associated complexities. Superdiversity is the future or, in many cases, the current reality of neighbourhoods, cities, countries and regions, yet the implications of superdiversification for governance and policy have, until now, received very little attention. First published as a special issue of Policy & Politics, this insightful volume brings together contributions from experts across Europe to explore the ways in which superdiversity has shaped the development of policy and to consider challenges for the future.