The book contains the main results of many years of research conducted in the Main Botanical Garden named after N.V. Tsitsin RAS in the field of studying the biological diversity of plants used in medicine, assessing the therapeutic properties and types of biological activity by the presence of certain biologically active substances in their composition. The material of the book is based on information collected by the authors about almost 12,000 species of flowering, gymnosperm plants, higher spores, algae, mosses, lichens, fungi with known biological activity, as well as about 1,500 biologically active compounds found in 6500 species of plants. The work offered to the reader is an attempt to combine and analyze many disparate data on various botanical issues related to the medical use of plants, including to facilitate the search for new medicinal plants. Medicinal possibilities of various ecological, geographical and systematic groups of kingdoms of plants and fungi are analyzed. For the first time, global retrospective reviews of national phytomedicines are given. Features of medicinal plants of island flora have been identified. The question was raised about the centers of origin of medicinal plants.