This is the first English translation of the ground-breaking study by the German medical doctor, psychotherapist, and mystic Carl Albrecht (1902-1965), first published in 1951 as Psychologie des Mystischen Bewußtseins. The book, reprinted in Germany in 1976, 1990 and 2018, has remained untranslated to date and is now made available to international scholarship in an annotated English edition. The book offers the results of Albrecht's meticulous long-term empirical research into mystical consciousness. Albrecht's results from a pioneering methodological approach based on 'Autogenic Training, ' which enabled a practitioner to verbalize spontaneously what he/she is experiencing while immersed in an altered state of consciousness. These spontaneous utterances of mystical (and non-mystical) experience were concurrently recorded by Albrecht and provided him with invaluable empirical data. The outcome was a most comprehensive, systematic, psychological phenomenology of mystical consciousness informed by long-term empirical research. Unlike other empirical studies in this field, which are either based on records of mystical experience retrieved retrospectively, derived from behaviorist research, or both, Albrecht's empirical data originate from immediate (not rationally mediated) verbal testimonies spoken by subjects while transported into a mystical state.