The study of plants and other natural sources in order to determine if they can be used to make drugs is known as pharmacognosy. It also includes the study of the physical, biochemical, chemical and biological properties of drugs along with its substances. It is mainly concerned with the analysis of natural product molecules that are useful for their medicinal, ecological and gustatory properties. It is a broad field that encompasses various biological subjects such as microbiology, marine biology, botany and herbal medicine. All plants produce phytochemicals during their normal metabolic activities. These chemicals are divided into primary and secondary metabolites. The primary metabolites include sugars and fats commonly found in all plants. The secondary metabolites are found in lesser number of plants and serve a more defined function. These can have therapeutic effects on humans, and can be refined to produce drugs such as quinine. This book contains some path-breaking studies in the field of pharmacognosy. It consists of contributions made by international experts. The book will serve as a valuable source of reference for graduate and post graduate students.