Why do animals play? Play has been described in animals as diverse as reptiles, birds and mammals, so what benefits does it provide and how did it evolve? Careful, quantitative studies of social, locomotor and object play behaviour are now beginning to answer these questions and to shed light on many other aspects of both animal and human behaviour. This unique interdisciplinary volume brings together the major findings about play in a wide range of species including humans. Topics about play include the evolutionary history of play, play structure, function and development, and sex and individual differences. Animal Play is destined to become the benchmark volume in this subject for many years to come, and will provide a source of inspiration and understanding for students and researchers in behavioural biology, neurobiology, psychology and anthropology.