Many people assume that experimentation with hallucinogens began with Timothy Leary and the psychedelic revolution of the fifties and sixties. In fact, as this illuminating study demonstrates, psychedelics have been used by human societies in every part of the world for ritual and spiritual purposes for millennia. As Paul Devereux points out, our modern culture is eccentric in its refusal to integrate the profound experiences offered by these natural substances into our own spiritual life and traditions. Modern Western culture's recent experimentation with psychedelic drugs raised the awareness of archaeologists and anthropologists, leading them to recognize the use of hallucinogens in surviving traditional societies and in the archaeological record. Devereux reveals dramatic new evidence - from linguistics, ethnobotany, biology, and other fields - for the psychedelic experiences of various prehistoric cultures, and ponders the implications and effects of psychedelic revelations on our contemporary worldview, linking them to out-of-body and near death experiencs, shamanic trances, even memory and dreaming.