Most textbooks and atlases of human anatomy chronicle only a few cases of muscle variations in the normal human population, or of muscle anomalies within congenital malformations. Consequently, there is a misconception of what is considered normal human anatomy and what that looks like. Each person within the normal population has at least a few muscle variations, and there are millions of individuals born globally each year with muscle anomalies. There are crucial knowledge gaps between what is taught, what students learn, what textbooks and atlases show, and what truly happens in nature and within our species. This handbook fills this gap by: 1) providing a comparative evolutionary context for muscle variations and defects in humans, 2) summarizing the major types of variations and anomalies found in humans, and 3) including didactic figures for a visually engaging learning experience. This book is of interest to students, professors, and researchers in biological anthropology, comparative anatomy, functional morphology, zoology, and evolutionary and developmental biology, as well as to clinicians and practicing health professionals.