There has recently been a renewed interest in both casual use of psychedelics as well as experimental use and attempts to discover therapeutic value. There is an effort to recapture the achievements and failures of past work to guide present use. This book is based around material derived from unpublished scientific research from Dr. Robert Mogar laboratory and built upon by forty years of field research by the author. The author Niccolo Caldararo participated in a number of studies of perception, including sensory deprivation and psychotropic drugs, some of recent manufacture or discovery and some of primitive or traditional societies. He places this analysis of the physiological aspects of hallucinations, delusions, visions and dreamsn context through an , as well as cross cultural data on dreams, dreaming and drug use and the social value of hallucinations, dreams and visions. The book reviews ethnographic literature in this area and contributes to a comprehensive evaluation of past work done in this area.