The earliest forms of life on Earth were plants. Remarkably preserved plant fossils have recently been discovered dating back 3.2 billion years. These early plants provided the foundation for the development of all later forms of plants and indeed of animals, including that most recent of creatures, the human being. The green plant cover of the earth has a marvelous relationship with the sun: chlorophyll-bearing plants absorb solar rays and synthesize organic compounds, the building materials for both plant and animal organisms. In vegetable matter, solar energy is stored in the form of chemical energy, source of all life processes. Thus the Plant Kingdom provides not only bodybuilding foods and calories but also vitamins essential for metabolic regulation. Plants also yield active principles employed as medicines. The intimate relationship between the human and plant world is easily discerned, but the production of substances profoundly affecting the mind and spirit is often not so easily recognized. These are the plants that make up the substance of Plants of the Gods, focusing attention on the origin of their use and the effect that they have had on man's development. Plants that alter the normal functions of the mind and body have always been considered by peoples in nonindustrial societies as sacred, and the hallucinogens have been " plants of the gods" par excellence.