Psychiatry and psychosomatic medicine are concerned with medical conditions affecting the brain, mind, and behaviour in manifold ways. Traditional approaches have focused on a restricted array of potential causes of psychiatric and psychosomatic conditions, including adverse experiences such as trauma, neglect, or abuse, genetic vulnerability, and epigenetic regulation of gene expression. While essential for the understanding of mental disorders, these approaches have disregarded pertinent questions such as why the human mind is vulnerable to dysfunction at all. This Textbook of Evolutionary Psychiatry and Psychosomatic Medicine seeks to find answers to these questions by emphasizing an evolutionary perspective on psychiatric and psychosomatic conditions. It explains how the human brain/mind has been shaped by natural and sexual selection; why adaptations to environmental conditions in our evolutionary past may nowadays work in suboptimal ways; and how human cognition, emotions, and behaviour can be scientifically framed to improve our understanding of how people try to attain important biosocial goals pertaining to one’s status in society, mating, eliciting and providing care, and maintaining rewarding relationships. The evolutionary topics relevant to the understanding of psychiatric and psychosomatic conditions include the concepts of genetic plasticity, life-history theory, stress regulation, and immunological aspects. In addition, it is argued that an evolutionary framework is necessary to understand how psychotherapy and psychopharmacology work to improve the lives of patients with psychiatric and psychosomatic disorders.