This book offers a new perspective on the philosopher, psychologist, and religious thinker William James. Using biographical materials, manuscripts, and analysis, the author develops the first systematic reading of James' world-view of radical empiricism, which sought to take concrete, immediate experience as the basis for understanding the world. The book offers close readings of key works by James. Lamberth argues that religion and philosophy themselves are intimately related conceptually for James; and concludes by relating James' conceptions to present debates concerning truth, religious experience, and theological understandings of the divine.