In the twenty-first century Pharmacognosy was transformed into a molecular science building on classic botanical and modern chemical knowledge, leading to a better understanding of the complex molecular effect - structure relationships and interactions required for the development of new drugs based on biologically active plant substances. The work demonstrates the place of phytotherapy in healing, the role of herbs in complementary and traditional therapy, and research strategies for the development of drugs of natural plant origin. This book is primarily designed for scientific researchers, but is also very useful for undergraduate and postgraduate students in their professional training. As this book discusses herbs from all over the world, it is specifically drafted to be useful not only in Hungary and Europe, but also for people in other continents as an English language encyclopaedia of medicinal plants and their biologically active compounds.