This text provides a concise introduction to the field of animal biology. Readers discover general principles of evolution, ecology, classification, systematics, and animal body plans. After these introductory chapters, readers delve into the biology of all groups of animals. The basic features of each group are discussed, along with evolutionary relationships among group members. Chapter highlights include newly discovered features of animals as they relate to ecology, conservation biology, and value to human society. Regular updates to the phylogenies within the book keep it current.