[This entry was originally titled "Buddhism, Schools of: Esoteric Buddhism" in the first edition of the Encyclopedia.]

Buddhist esotericism is an Indian movement obscure in its beginnings. Combining yoga and ritual, it calls itself the Diamond Vehicle (Vajrayāna)—where diamond means "the unsplittable"—or the Mantra Vehicle (Mantrayāna)—where mantra means "magical speech." The revealed texts of the tradition are called tantra, in contrast to sūtra (the generic name of the non-Tantric Buddhist scriptures), but both these words have the implication "thread" or "continuous line." In the case of the Tantras, the "continuous line" can be understood in various ways: the lineage of master-disciple, the continuity of vows and pledges in the practitioner's stream of consciousness, or the continuity of practice leading to a religious goal.

Much of Tantric literature is ritualistic in...