Abstract In Varieties of Religious Experience: A Study in Human Nature (1902) William James examines the role of mysticism in the development of religion. James argues that the root of all religions is precisely the experience of mystical states of consciousness. As we shall see, although James himself admits that his own psychological constitution shuts him out from these experiences, the acknowledgement of practical developments of mysticism within institutionalized religions illustrates the reality of these states of consciousness, a stance supported by James’ pragmatism. Thus, the paper not only examines the nature of mysticism but presents James’ pragmatist view of religion.