Natural bioactive compounds have become an integral part of plant—microbe interactions geared toward adaptation to environmental changes. They regulate symbiosis, induce seed germination, and manifest allelopathic effects, i.e., they inhibit the growth of competing plant species in their vicinity. In addition, the use of natural bioactive compounds and their products is considered to be suitable and safe in e.g. alternative medicine. Thus, there is an unprecedented need to meet the increasing demand for plant secondary metabolites in the flavor and fragrance, food, and pharmaceutical industries. However, it is difficult to obtain a constant quantity of compounds from the cultivated plants, as their yield fluctuates due to several factors including genotypic variations, the geography, edaphic conditions, harvesting and processing methods. Yet familiarity with these substances and the exploration of various approaches could open new avenues in their production. This book describes the basis of bioactive plant compounds, their mechanisms and molecular actions with regard to various human diseases, and their applications in the drug, cosmetic and herbal industries. Accordingly, it offers a valuable resource for students, educators, researchers, and healthcare experts involved in agronomy, ecology, crop science, molecular biology, stress physiology, and natural products.