Brewed from a combination of two plants--the leaves of Psychotria viridis and the vine stalks of Banisteriopsis caapi--ayahuasca has been used for millennia by indigenous tribes throughout the Upper Amazon for healing and spiritual exploration. The shamans of the Peruvian Amazon call the plant spirit within the vine Abuela Ayahuasca, Grandmother Ayahuasca. She is said to be a mother spirit of nature who provides guidance and healing to those who work with her. Exploring the history, lore, traditional use, psychoactive effects, and current scientific studies of this powerful hallucinogen, Christian Funder reveals how Grandmother Ayahuasca is a profound healer, wise teacher, and life-changing guide. Examining ayahuasca from a neuroscientific perspective, the author looks at recent research on the effects of DMT--one of the psychoactive compounds in ayahuasca--as well as fMRI studies of brain activity during altered states. He explores these findings as they relate to the teachings on unified states of consciousness in ancient esoteric texts and to Aldous Huxley's theory of psychedelics inhibiting the "reducing valve" mechanism of the brain. Sharing interviews with people who have experienced ayahuasca's powerful "spirit doctor" effects, Funder also details his own revolutionary ayahuasca healing journey from suicidal depression to a soul at peace. He explores ayahuasca's relationship to indigenous Amazonian shamanism, including an inside look at the Shipibo tribe and the healing songs known as icaros. Drawing on the work of Jeremy Narby, he investigates the consciousness of nature that shamans access through the use of ayahuasca and other ancient plant medicines such as San Pedro. Offering a holistic picture of ayahuasca--from science to spirit--the author shows that this venerated hallucinogenic tea has immense therapeutic potential and just might be the long-lost shamanic connection to the sacred Gaian mind.