This volume introduces what has sometimes been called "the third component of western culture." It traces the historical development of those religious traditions that rejected a worldview based on the primacy of pure rationality or doctrinal faith, emphasising instead the importance of inner enlightenment or gnosis: a revelatory experience that was typically believed to entail an encounter with one's true self as well as with the ground of being, God.

The contributions to this book demonstrate that this perspective is fundamental to a variety of interconnected traditions. In antiquity, one finds the gnostics and hermetics; in the Middle Ages several Christian sects. The medieval Cathars can, to a certain extent, be considered part of the same tradition. Starting with the Italian humanist Renaissance, hermetic philosophy became of central importance to a new religious synthesis that can be referred to as "Western Esotericism." The development of this tradition is described from Renaissance hermeticists and practitioners of spiritual alchemy to the emergence of Rosicrucianism and Christian Theosophy in the seventeenth century, and from post-Enlightenment aspects of Romanticism and occultism to the present-day New Age movement.