It has been known for a relatively long time that the microbes living in our gut play an important role in regulating our physical and mental health. However, recent literature emphasizes the potentially major role of the gut microbiome in the regulation of brain function and behavior. Gut microbes play an important role in the development and regulation of behavior and cognition, giving rise to a connection between the brain and the gut, also known as the gut-brain axis. Conversely, the social behavior of the host itself will directly influence the composition of the gut microbiome, indicating the axis is bidirectional. To date, very little is known about the gut-brain axis in animals, especially in non-human primates. Great apes are of particular interest, since they form an excellent study system to investigate the evolution of the gut-brain axis in humans because of their high evolutionary relatedness. Bonobos in particular form an interesting model-species due to their high overlap in socio-cognitive skills with humans, but surprisingly, their gut microbiome remains largely unstudied. Therefore, the aim of this study is to characterize the bonobo gut microbiome and to investigate which factors drive interindividual variation in gut microbiome composition and diversity, including behavior. Moreover, I will perform behavioral observations combined with experimental microbiome manipulations to closely examine the impact and dependence of the microbiome on bonobo sociality.