This book is a reassessment of how immigration is changing our world. The policies of multiculturalism that were implemented in the wake of postwar immigration have, after 9/11, come under intense scrutiny, and the continuing flow of populations has helped to ensure that immigration remains high on the social and political agenda. Based on his deep knowledge of the European and American experiences, the author shows how immigration entails the loss of familiar worlds, both for immigrants and for host societies, and how coming to terms with a new environment evolves from avoidance through conflict to accommodation. The conflict that accompanies all major migratory movements is not a failure of integration but part of a search for new ways to live together. It prompts an intensive process of self-examination. That is why immigration has such a profound existential impact: it goes to the heart of institutions like the welfare state and liberties like the freedom of expression. The author argues that our ability to cope with the challenges posed by immigration requires that we move beyond multiculturalism and find a new balance between openness and exclusion. Tolerance cannot be based on avoidance but should rest on the principle of reciprocity, which means that native populations cannot ask of newcomers any more than they themselves are prepared to contribute.