The importance of kinship for human societies has long been recognized, indeed the interest in kinship is reflected in the large number of works, plays, books, operas, etc., which have kinship, often mistaken, as their central theme. Whilst there has been little doubt that humans recognize their kin and respond differentially to them, the ability of animals to recognize and respond differentially to kin has received little attention. In recent years, however, study of the influence of kinship on the social behaviour of animals has increased dramatically. Much of the impetus for this research can be attributed to the seminal works of Hamilton (1964a,b) and later Wilson (1975). Evidence that kinship, or genetic relatedness, influences an individual's behaviour has now been documented in all the major groups of animals – from single-celled organisms (e.g. Grosberg & Quinn, 1986) to man (e.g. see Porter, this volume). Reptiles remain an exception to this and only recently have studies appeared providing evidence of kin recognition in this group (e.g. Werner et al, 1987), which probably reflects a lack of empirical investigation rather than a lack of ability to recognize kin. As diverse as the groups of animals which exhibit evidence of kin recognition are the behaviours in which individuals respond differentially on the basis of kinship; colonization patterns, mating, play, aggression, feeding, schooling, swarming, defence, etc. all are influenced by kinship. Investigations of the ability to recognize kin have revealed that individuals have well developed capabilities to recognize kin; siblings, half-siblings, cousins, parents, offspring, grandparents, aunts and uncles are all capable of being discriminated. Kinship thus appears to influence behaviour throughout the animal kingdom.