Overview of the current state of scientific knowledge about social evolution in ants, which also shows how studies on ants have contributed to an understanding of many fundamental topics in behavioural ecology and evolutionary biology. One of the substantial contributions of this volume is its clear explanation of kin selection theory and sex ratio theory and their applications to social evolution in insects. Working to dispel lingering scepticism about the validity of kin selection, and more broadly, of `selfish gene' theory, the authors argue that these ideas underpin the evolution of both cooperation and conflict within ant societies. Two relatively little known topics in ant social biology are also briefly discussed: life history strategy, and mating systems.