Cooperation between the sexes in the rearing of offspring is rare in the animal kingdom, but typical of most species of birds. The usual form of cooperation in birds is for the male and female of a monogamous pair to invest more or less equally in the defense of a breeding area and in the care of young. Thus, most species of birds are cooperative breeders, but this cooperation is limited strictly to the breeding pair, and other conspecifics are vigorously excluded from the vicinity of the nest and young. I therefore use the term ‘cooperative breeding’ in the restricted sense used elsewhere in this book (see Introduction to this volume).

My perspective in this summary is that of a student of the behavior and population biology of typical birds, i.e. those that cooperate only with a mate while reproducing. Thus, I approach the subject without biases from having worked on a cooperatively breeding species. I first review briefly some questions about cooperative breeders, and the kinds of data that are needed to address them. I then consider how far these questions have been answered by the studies in the book. I conclude by noting that studies of cooperative breeders have enhanced our general understanding of the population biology of birds, and I suggest some directions for future work.