The purpose of this thesis is to present data on the social interactions among ten adult baboons, and to show how these interactions are affected by changes in the female reproductive state. Using data on social interactions , I attempt both to describe social relationships and t o suggest how such relationships may contribute to social structure (Hinde in press) . Throughout the thesis, I am concerned with the following three general questions: (1) what are the advantages, to each individual, of life in a social group? (2) how do individuals adjust their behaviour with respect to others? (3) What pr inciples , governing the social behaviour of adults in one troop of baboons, might aid in our understanding of social bonds and social structure in other primate species? These are broad, theoretical questions, and I cannot claim that my research has yielded more than t entative answers to them. In particular , I would like to emphasize the limitations inherent in the study of a single troop, where the blood relations of animals could not be determined (see also Chapter Two, Section II., A. ). In justification of my approach, however, I feel that the social organization and behaviour of free- ranging primates are the result of natural selection acting on individuals through both their physical and their social environments. Moreover, while studies of feeding, ranging, and group composition have provided one perspective from which to view primate societies, I feel that an analysis of social bonding among adults may well provide another .