This book offers a radical new reading of William Jamess work on the idea of religion. Moving beyond previous psychological and philosophical interpretations, it uncovers a dynamic, imaginative, and critical use of the category of religion. This work argues that we can only fully understand Jamess work on religion by returning to the ground of his metaphysics of relations and by incorporating literary and historical themes. It will be a benchmark text in the reshaping of James and the nineteenth-century foundations of the modern study of religion.