William James’s Varieties of Religious Experience (1902) occupies a foundational position within the depth-psychology corpus, functioning simultaneously as a primary source, a historical landmark, and a live theoretical touchstone. Delivered as the Gifford Lectures at Edinburgh in 1901–02, the work arrived at the cusp of the Uranus-Neptune opposition that Tarnas identifies with a broader cultural awakening to the numinous, and its empirical, phenomenological method directly shaped Rudolf Otto’s concept of the holy and, crucially, C. G. Jung’s psychology of religious experience. The corpus records James’s influence operating along two distinct axes: the intellectual-historical, tracing how his typology of conversion, mystical states, and the ‘subconscious self’ migrated into Jungian analytic theory; and the applied-therapeutic, documenting how his findings on ‘deflation at depth’ and spiritual transformation became structural pillars of Alcoholics Anonymous through Bill Wilson’s direct reading of the text. Tensions within the corpus cluster around James’s pragmatic pluralism—his insistence that religious phenomena be judged by fruits rather than roots—set against both Freudian reductionism, which dismissed such experience as illusion, and later transpersonal researchers such as Grof and Yaden, who extended James’s comparative project into pharmacological and neuroscientific domains. The work’s enduring significance lies in its refusal to evacuate religious experience of psychological reality while simultaneously resisting dogmatic metaphysics.