It is hoped that the following pages will demonstrate something of the essential interplay between nature and culture—between chemistry, mind set, and social and historical setting—in the use of hallucinogenic plants and other psychoactive substances by different peoples the world over. Obviously, many significant areas of research in psychopharmacology and ethnobotany, as well as some interesting and as yet little understood nonchemical "techniques of ecstasy" have had to be slighted, in favor of indepth treatment of some others of more general interest. Besides, this is an ongoing story: "new" botanical hallucinogens and other naturally occurring psychoactive substances — some perhaps never culturally exploited, others long forgotten by the people who formerly used them, and yet others successfully concealed for centuries from the prying eyes of outsiders — are even now being discovered and scientifically described and tested. Still more await botanical and pharmacological identification beyond the native terms under which they appear in the ethnohistorical literature or reports of travelers and ethnographers. Even for Indian Mexico or Amazonia, whose extensive psychoactive pharmacopoeia has been relatively well studied, we still do not know the identity of every species used in native ritual, prehistorically or at present, nor do we as yet fully understand the pharmacological or cultural role of additives to plants of known or suspected psychoactivity. Indeed, in the opinion of such authorities as Richard Evans Schultes, Director of Harvard's Botanical Museum, it is precisely the function of these additives to the botanical hallucinogens that presents one of the most exciting challenges to the modern investigator of the psychedelic phenomenon in indigenous societies. Clearly, then, there is a world yet to be discovered. The concerned reader is urged to keep up with the more specialized ethnobotanical publications and the rapidly growing literature on brain biochemistry and scientific and humanistic explorations into the uses and abuses of alternate states of consciousness.