Beginning in the fifth century A.D., various Indian mystics began to innovate a body of techniques with which to render themselves immortal. These people called themselves Siddhas, a term formerly reserved for a class of demigods, revered by Hindus and Buddhists alike, who were known to inhabit mountaintops or the atmospheric regions. Over the following five to eight hundred years, three types of Hindu Siddha orders emerged, each with its own specialized body of practice. These were the Siddha Kaula, whose adherents sought bodily immortality through erotico-mystical practices; the Rasa Siddhas, medieval India's alchemists, who sought to transmute their flesh-and-blood bodies into immortal bodies through the ingestion of the mineral equivalents of the sexual fluids of the god Siva and his consort, the Goddess; and the Nath Siddhas, whose practice of hatha yoga projected the sexual and laboratory practices of the Siddha Kaula and Rasa Siddhas upon the internal grid of the subtle body. For India's medieval Siddhas, these three conjoined types of practice led directly to bodily immortality, supernatural powers, and self-divinization; in a word, to the exalted status of the semidivine Siddhas of the older popular cults. In The Alchemical Body, David Gordon White excavates and centers within its broader Indian context this lost tradition of the medieval Siddhas. Working from a body of previously unexplored alchemical sources, he demonstrates for the first time that the medieval disciplines of Hindu alchemy and hatha yoga were practiced by one and the same people, and that they can only be understood when viewed together. Human sexual fluids and the structures of the subtle body aremicrocosmic equivalents of the substances and apparatus manipulated by the alchemist in his laboratory. With these insights, White opens the way to a new and more comprehensive understanding of the entire sweep of medieval Indian mysticism, within the broader context of south Asian Hinduism, Buddhism, Jainism, and Islam. This book is an essential reference for anyone interested in Indian yoga, alchemy, and the medieval beginnings of science.