It was a both philosopher and experimental psychologist that William James approached the study of religious phenomena. Conversion, repentance, mysticism, hopes of reward and fears of punishment in the hereafter are studied by him with boldness, sympathy and the unbiased common sense of science. The result is a book that has become a living force in religious literature, for believer and non-believer alike, and has contributed to William James's stature as a great American philosopher.