The tension between naturalism and religion is the central theme of this major new book by Jürgen Habermas. On the one hand he argues for an appropriate naturalistic understanding of cultural evolution that does justice to the normative character of the human mind. On the other hand, he calls for an appropriate interpretation of the secularizing effects of a process of social and cultural rationalization increasingly denounced by the champions of religious orthodoxies as a historical development peculiar to the West. These reflections on the enduring importance of religion and the limits of secularism under conditions of postmetaphysical reason set the scene for an extended treatment of the political significance of religious tolerance and for a fresh contribution to current debates on cosmopolitanism and a constitution for international society.