Twenty-first-century Europe has become the scene of very contrasting tendencies where religion is concerned. These include secularization and religious revival and declining Christianity and the rise of immigrant religions, particularly Islam. The ongoing European integration and enlargement of the European Union eastward encourages discussions on the religious foundations of Europe and on its geographical boundaries. The close connection between political and religious developments has made historical processes of state formation and nation building relevant to understanding the existing variety of state-church relations and the different reactions to the rise of immigrant religions or the post-communist religious revival. The book focuses on religious development in the different countries of Europe and includes case studies from ten countries. These case studies look on three topics: the changing religious composition of the population; the geographical distribution of the religious communities involved; and the changing state-church or state-religion relationships.