This book delves into the intricate journey of neuroendocrine evolution, from its rudimentary origins in single-celled organisms to the complex systems found in mammals. It offers a comprehensive exploration of how neuropeptides and their receptors have evolved, highlighting the pivotal role of the hypothalamus and pituitary gland in this process. Key concepts covered include the evolution of neuropeptide signaling, insights from invertebrate hypothalamic-pituitary systems, and the functional trajectories of ancient peptide ligand-receptor systems. The book addresses critical questions such as the organization and evolution of neurotransmitter volume transmission, the form and function of growth hormone-releasing hormone across vertebrates, and the co-evolution of neuroendocrine signaling dyads. Chapters on the melanocortin system, corticotropin-releasing hormone, and nonapeptide regulation of social behavior in teleost fish provide a deep dive into specific pathways and their evolutionary significance. Aimed at researchers and professionals in neuroscience, endocrinology, and evolutionary biology, this text serves as an invaluable resource for anyone interested in the comparative anatomy and physiology of neuroendocrine systems. This is the seventeenth volume in the International Neuroendocrine Federation (INF) Masterclass in Neuroendocrinology series, which aims to illustrate the highest standards and highlight the latest technologies in basic and clinical research, and aspires to provide inspiration for further exploration into the exciting field of neuroendocrinology.