In the last decade, melanocortin biology has matured. Three additional receptors were discovered, and animal models were established addressing the function of each receptor. Researchers now know that the diverse physiologic responses to melanocortins—including their role in development, weight and endocrine regulation, cortisol production, secretion from exocrine glands, and pigmentation—can be defined in terms of individual receptors. In this volume, contributors from the fields of evolutionary biology, peptide chemistry, pigmentation biology, neuroscience, endocrinology, and genetics provide the reader with a comprehensive review of melanocortin biology. Six areas of active research are addressed: peptide and small molecule chemistry; receptor structure and function; energy homeostasis; pigmentation; adrenocortical function; and behavior.