Old World monkeys (Cercopithecoidea) are the most successful and diverse group of living nonhuman primates in terms of the number of species, behavioral repertoires, and ecology. Among our closest living relatives, they have much to teach us about the processes of evolution and the principles of ecology. This volume presents a broad, technical account of cercopithecoid biology including molecular, behavioral, and morphological approaches to phylogeny, population structure, allometry, fossil history, functional morphology, ecology, cognitive capabilities, social behavior, and conservation. It will be the definitive reference on this group for researchers, graduate students and advanced undergraduates in primatology, animal behavior, paleontology, morphology, systematics, and physical anthropology.