The third edition of Hormones will provide a comprehensive treatment of the hormones of humans and brief summaries of the hormones of plants and insects, all viewed from the context of modern theories of their action in the framework of our current understanding their molecular structures and physiological functions. This new edition is intended to be used principally by advanced undergraduates and graduate students in the biological sciences. As the field of endocrinology itself has expanded so much in the past two decades, the up-to-date presentation of the basics planned for this book will be a solid foundation on which more specialized considerations can be based. The revised Hormones will presume that the reader will have been exposed in detail to the areas of knowledge fundamental to biochemistry, including the structure and function of macromolecules and the other bioorganic substances of intermediary metabolism, as well as to a wide array of topics in molecular biology. In addition, an understanding of cell biology, cellular and subcellular organization, and mammalian physiology will be useful. It is the pentad of biochemistry, structural biology, molecular biology and cell and organ physiology that forms the foundation for the principals of the biological facts of life that are critical to the development of our modern understanding of the molecular endocrinology of hormones and their actions. The book is organized to provide two introductory chapters followed by 20 chapters on selective endocrine topics. In this third edition, two previous chapters have been eliminated: The material in separate chapter on the Hypothalamus (2nd Edition) has been integrated with the anterior pituitary because of the intimate functional and relationship between the two. The chapter on the thymus has been eliminated as more properly belonging in a book on immunology. The authors have added two new chapters (19 and 20) to introduce the student to the world of plant and insect hormones. Each of these areas occupies a unique niche in our understanding of the biological world and is part of the universality of signalling systems and how they govern biological systems.