Anthropological studies of religion have been largely concerned with belief, with ritual, and with the general integrative significance of religious institutions for society. But many issues in the power relations of religious affiliation are still not clear. The political implications of religion involve grave practical as well as theoretical problems. Abstractly, religion and politics are often conceived as opposed; concretely, they interact. While religion can be a powerful political instrument, it can also adapt to political ends and generate its own political structures. In contrast to the broadly affirmative role assigned by anthropologists to religion in society is Karl Marx’s thesis of religion as political ideology. Reasons for granting some validity to this position but also for questioning its basic assumptions are given. The whole analysis is illustrated by a wide range of examples, from Polynesian ethnography to the history of Christianity and of Islam, and the situation of religion in modern socialist states.