This book attempts to present the subject of religious mysticism to both the technical student and the lay reader at one and the same time. The latter will find no annoyance, however, in details which appear for the former’s sake. Transliterations are for the most part, in the forms used by authorities quoted. The spellings, Mohammed, Moslem, Koran, and a few others are retained, where possible, in their most familiar forms. The dates enumerated are of the Christian era, unless otherwise indicated.