Many of the most fascinating and dramatic examples of animal behaviour involve collective activities. These include the synchronised movements of large flocks of birds and shoals of fish, the complex and efficiently regulated organisation of bee colonies, and the intricate, and often monumental, structures built by termites. Such phenomena can hardly fail to astonish and interest. However, they are also important because many of the mechanisms and principles underlying them seem to apply to our own, human, collective behaviours.