Widely recognized by anthropologists as the most powerful and widespread shamanic hallucinogen, ayahuasca has been used by native Indian and mestizo shamans in Peru, Colombia, and Ecuador for healing and divination for thousands of years. Made from the Amazonian vine Banisteriopsis caapiand the DMT-laden leaf of Psychotria viridis, ayahuasca is regarded as the embodiment of intelligent plant beings who can offer spiritual teachings and healing knowledge to those who respectfully engage with them. Many Western-trained physicians and psychologists now acknowledge that ayahuasca allows access to spiritual dimensions of consciousness, otherworldly realms and beings, and visionary experiences indistinguishable from classic religious mysticism. With contributions from leading psychoactive scholars Dennis J. McKenna, Ph.D., Charles S. Grob, M.D., and J. C. Calloway, Ph.D., on the ethnopharmacology, psychology, phytochemistry, and neuropharmacology of ayahuasca, Ralph Metzner provides a comprehensive exploration of the chemical, biological, psychological, and experiential dimensions of this Amazonian hallucinogen. He includes more than 20 firsthand accounts from people who have participated in ayahuasca rituals and experienced major life changes as a result. He details the scientific discovery of ayahuasca’s sophisticated psychoactive delivery system in the brain and body as well as the deep psychological impact of this potent entheogen. He concludes with his own findings on ayahuasca, including its applications in medicine and psychology, and compares the worldview revealed by ayahuasca visions to that of modern cultures.