This book proposes a way to radically renew medicine by extending to medicine the concepts of evolutionary biology. The book considers diseases not as unpredictable harmful events but as logical consequences of evolutionary mechanisms. In particular, a large part of the most widespread diseases that afflict modern populations are interpreted as the consequence of discordances (mismatches) between new living conditions and the adaptation of our species. It discusses the basic concepts, as well as diseases deriving from alterations of the genotype and general concepts about diseases deriving from alterations of the ecological niche. It also describes diseases deriving from relations with other living beings especially when the ecological niche is altered, diseases deriving from conditions beyond the adaptation range, and physiological phenomena that cause troubles and suffering or even death. A particular study is dedicated to the interpretation of aging and its consequences in normal or altered conditions of the ecological niche. The final part of the book describes the implementation of evolutionary medicine. This book, complementing the "Evolutionary Gerontology and Geriatrics" book, which is also published in this series, provides a valuable read for scholars and students in the fields of medicine, evolutionary biology, preventive medicine, and gerontology.