Which plants have been included in this encyclopedia? I considered all of those plants that my own research and experience have indicated to be psychoactive as well as those plants that other researchers or the literature have reported to be psychoactive. Here, we must keep in mind that there are plants for which a majority of subjects have reported no psychoactive effects. There also are plants that have a reputation of being hallucinogenic, but which no one has yet tried. To date, many of these plants have been the object of only cursory investigation. There also are a number of plants that have not yet been botanically determined or identified. The situation is complicated by the fact that the botanical data contained in the ethnographic literature are often incorrect, or at least very imprecise. Sometimes, it was difficult to decide whether a particular plant should be included in this work or not. One such case is St. John’s wort (Hypericum perforatum L.), which the ancient Germans used as a sedative and in modern phytotherapy is generally regarded as a natural tranquilizer (Becker 1994). St. John’s wort and the oil it yields do indeed exert a psychoactive effect, but only upon patients suffering from mental or emotional afflictions. As a rule, healthy individuals do not notice any psychotropic effects, even after ingesting large amounts. 14 Such uncertain cases—to the extent that they are known—have not been included in these monographs. Reflecting our current state of knowledge, I have treated the various psychoactive plants discussed in this book in several different ways. Well-known plants that have been investigated in some detail are examined in a very systematic fashion in the major monographs. Plants that have been little studied or about which very little is known are discussed in informal minor monographs. A number of very well-known and wellresearched plants that are purported to produce psychoactive effects and are sometimes referred to as “legal highs” are considered in their own small section of informal monographs. This is followed by another section that focuses on a number of psychoactive plants whose botanical identity is unknown. Because they are not plants in the strict sense, psychoactive fungi are presented in a section of their own. The section on psychoactive fungi is followed by another that focuses on psychoactive products that are obtained through often intricate procedures and/or from combinations of plants. Finally, there is a short section that examines the psychoactive constituents of plants. This section also serves as an aid in locating the plants discussed in the monographs.