This book focuses on hormones, and on how they are produced in very diverse regions of the body in humans and animals. Hormones exhibiting the same synthesis pathways are not only found in vertebrates, but also in insects, shellfish, spiders, mollusks, and they were present evenat the time of metazoan diversification. The book discusses the different classes of hormones: protein/peptides hormones, steroids and juvenile hormones and hormones like catecholamines, thyroid hormones and melatonin. It also discusses the different types of hormone receptors, the majority of which are heptahelical G-protein coupled receptors or nuclear receptors. Particular attention is paid to the organs where hormones are synthesized, with specifics on production and release, while a dedicated chapter details hormonal regulation in systems ranging from the very simple to the highly complex. The remarkable kinetics of hormone production is also shown, and the book is rounded out by chapters on the evolution of the endocrine system, the genetics of endocrine diseases and doping.