Primate societies have been classified into discrete categories based on the flexibility of their social organisation. However, due to growing evidence of intra-specific and temporal variation in grouping patterns, it has been suggested that instead, primate societies should be characterised by their relative degree of fission-fusion dynamics, which indicates the extent to which groups vary in spatial cohesion and the temporal variation in the size and composition of parties. While perceived predation risk and food availability are known to be key factors shaping primate societies, it is not clear if fission-fusion dynamics reflect short-term behavioural adaptations to these factors, and if social preferences also influence fission-fusion dynamics. Furthermore, little is known about the impact of fission-fusion dynamics on social relationships. These issues are addressed in this thesis by investigating the grouping patterns and social relationships of two troops (Gamgam and Kwano) of free-ranging olive baboons (Papio& hamadryas & anubis) in Gashaka-Gumti National Park, Nigeria. Grouping patterns were measured through association networks and the temporal variation in party size, party composition, and spatial cohesion, and were related to variations in food availability, predation risk, and habitat use. Variations in patterns of associations and fission-fusion dynamics were found both between troops, and between seasons within troops. As these variations could largely be accounted for by differences in ecology and demography, it seems that fission-fusion dynamics reflect a short-term optimisation of the trade-off between the cost and benefits of group living. The network of associations of the fluid Kwano troop, but not of the cohesive Gamgam troop, was found to be sub-structured in a way that indicates Infanticide avoidance may play an important role in association patterns. Both the frequencies of social behaviours, and the structures of networks based on five types of social interactions, were related to differences in fission-fusion dynamics. The degree of fission-fusion dynamics appears to influence social relationships, as a quantitative difference in social behaviour was linked to variation in fission-fusion dynamics.