Cooperative breeders are species in which more than a pair of individuals assist in the production of young. Cooperative breeding is found in only a few hundred bird species world-wide, and understanding this often strikingly altruistic behaviour has remained an important challenge in behavioural ecology for over 30 years. This book highlights the theoretical, empirical and technical advances that have taken place in the field of cooperative breeding research since the publication of the seminal work Cooperative Breeding in Birds: Long-term Studies of Behavior and Ecology (1990, HB ISBN 0521 372984, PB ISBN 0521 378907). Organized conceptually, special attention is given to ways in which cooperative breeders have proved fertile subjects for testing modern advances to classic evolutionary problems including those of sexual selection, sex-ratio manipulation, life-history evolution, partitioning of reproduction and incest avoidance. It will be of interest to both students and researchers interested in behaviour and ecology.