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