The present book aims to provide a comprehensive overview of the sources, extraction methods, chemical characterization, and biological activities of plant-derived bioactive compounds. It highlights how advances in phytochemistry, analytical techniques, and biotechnology have enhanced our understanding of the medicinal value of herbal resources. This work is designed to bridge the gap between traditional knowledge and modern scientific validation. Special emphasis has been placed on the role of phytochemicals such as alkaloids, flavonoids, phenolics, terpenoids, and glycosides in disease prevention, therapeutic applications, and nutraceutical development. The book also discusses safety considerations, standardization, and future prospects for herbal drug discovery.