This wide-ranging textbook provides a broad overview of the current state of animal behavior studies. It is an ideal textbook for undergraduate and graduate courses in biology, experimental psychology and neuroscience. It comprises a series of contributions from international experts. It represents a diverse set of approaches to animal behavior. It ranges across the subject all levels, from molecules and neurons to individuals and populations. It draws on the work of the pioneering Dutch ethologist, Niko Tinbergen. It addresses all four of Tinbergen's key questions: causation, development, function, and evolution. It deals with contemporary subjects, such as animal welfare, conservation, neurobiology, and animal cognition.