This textbook helped to define the field of Behavioural Ecology. In this fourth edition the text has been completely revised, with new chapters and many new illustrations and colour photographs. The theme, once again, is the influence of natural selection on behaviour - an animal’s struggle to survive and reproduce by exploiting and competing for resources, avoiding predators, selecting mates and caring for offspring, - and how animal societies reflect both cooperation and conflict among individuals. Written in the same engaging and lucid style as the previous editions, the authors explain the latest theoretical ideas using examples from micro-organisms, invertebrates and vertebrates. There are boxed sections for some topics and marginal notes help guide the reader. The book will be essential reading for students of behavioural ecology, animal behaviour and evolutionary biology.