Hominin-cercopithecid comparisons have been used in palaeoanthropology for over forty years. Fossil cercopithecids can be used as a ‘control group’ to contextualize the adaptations and evolutionary trends of hominins. Observations made on modern cercopithecids can also be applied to questions about human evolution. This article reviews the history of hominin-cercopithecid comparisons, assesses the strengths and weaknesses of cercopithecids as comparators in studies of human evolution, and uses cercopithecid models to explore hominin inter-specific dynamics. Cercopithecids appear to be excellent ecological referents, but may be less good when considering the cognitive abilities and cultural adaptations of hominins. Comparison of cercopithecid and hominin adaptations at Koobi Fora in East Africa indicates that, whereas the cercopithecids were largely grass- or leaf-eating, the hominins occupied a generalist niche, apparently excluding other primate generalist-frugivores. If any of the hominin species at Koobi Fora were sympatric, analogies with modern cercopithecids suggest that inter-specific contact cannot be discounted and may even have been beneficial.