The relation of science to secularisation is discussed in relation to the sociological frameworks of rationalisation and social differentiation in the context of cross-national and cross-cultural comparison. It is argued that there is no consistent relation between the degree of scientific advance and a reduced profile of religious influence, belief and practice. The crucial factors are sociological and historical, in particular the relation of religion to power and to the role of the intelligentsia in promoting radical social change. It is also argued that mental space constitutes a manifold so that there is in principle no zero-sum relation between science and religion. That there is such a relation derives from the Enlightenment master narrative and it acquires much of its emotional power not from the logical consequences for religion of science as from a putative relation between religion and moral evil and the legitimation of oppressive regimes. However there are indirect consequences of science for religion through the social consequences of technological change. In practice the consequences of historical studies, for example biblical criticism, are probably greater than the consequences of science.