Originally published in 1973. The volume is divided into four sections: * The introduction places the position of the Buddhist Tantras within Mahayana Buddhism and recalls their early literary history, especially the Guhyasamahatantra; the section also covers Buddhist Genesis and the Tantric tradition. * The foundations of the Buddhist Tantras are discussed and the Tantric presentation of divinity; the preparation of disciples and the meaning of initiation; symbolism of the mandala-palace Tantric ritual and the twilight language. * This section explores the Tantric teachings of the inner Zodiac and the fivefold ritual symbolism of passion. * The bibliographical research contains an analysis of the Tantric section of the Kanjur exegesis and a selected Western Bibliography of the Buddhist Tantras with comments.