Humans live in large and extensive societies and spend much of their time interacting socially. Likewise, most other animals also interact socially. Social behaviour is of constant fascination to biologists and psychologists of many disciplines, from behavioural ecology to comparative biology and sociobiology. The two major approaches used to study social behaviour involve either the mechanism of behaviour - where it has come from and how it has evolved, or the function of the behaviour studied. With guest articles from leaders in the field, theoretical foundations along with recent advances are presented to give a truly multidisciplinary overview of social behaviour, for advanced undergraduate and graduate students. Topics include aggression, communication, group living, sexual behaviour and co-operative breeding. With examples ranging from bacteria to social mammals and humans, a variety of research tools are used, including candidate gene approaches, quantitative genetics, neuro-endocrine studies, cost-benefit and phylogenetic analyses and evolutionary game theory.