Mystical phenomena in intellectual and psychophysiological manifestations are well summarized. Revelation is considered visual, corporal, imaginary, and perceptual. Physiological correlates, from sensations of levitation and prolonged abstinence to ecstasy, are studied. Mysticism is considered a special type of psychological experience which expands the ego but also, because of its value as a defense mechanism, preserves the sense of identity and retains contact with reality. It is considered to be not simply a religious experience, but a more general psychological manifestation which could lead to such pathological phenomena as hallucinations. Before it can be considered a defense or the breaking through of repressed material, one must take into consideration the total personality of the 'mystic'.