Based on modern data and concepts, the book examines intercellular control systems and their interrelation; topography and morphology of the endocrine glands; organization of endocrine functions; chemical structure of hormones, their biosynthesis, secretion, transport, metabolism, mechanisms of their action on cells. This publication (the first one came out in 1980) is supplemented with the latest information on various questions of endocrinology. The book underlines scientific and practical importance of endocrinology for medicine and agriculture. The textbook is written based on the university course in endocrinology and the physiology of metabolism approved of by the Presidium of the Scientific and Methodological Council for Higher Biological Education of the State Committee for Higher Education. It is primarily designed for biology students and beginning researchers in the field of physiology of the endocrine system and biochemistry of hormones. The author hopes that this publication will also be of use to all those who are interested in endocrinology and intercellular interactions.