The non-human primates are a diverse group, with new species recognised every year. Most arise from re-classification, as scientists recognise new morphs, identify genetic clusters and map groups with different ecologies or social systems within existing species. This seems to occur particularly frequently among the Platyrrhini, who are generally less well known than the African and Asian monkeys. Plecturocebus parecis, for instance, was described in December 2019 and represents the twentieth new monkey from Brazil alone since the year 2000. At the same time as we are increasingly recognising more and more finely-divided species, however, we are also forced to confront the fact that many of these species overlap and interbreed. Some self-sustaining hybrid zones, like that between geladas and Papio baboons in Ethiopia, have been known for decades, with hybrid individuals recognisable on sight. In other cases, we know about extensive past hybridisation only from genetic analysis. Both lines of evidence suggest that species boundaries in the Order Primates are often leaky, and that reticulation may be a source of evolutionary innovation, not just an occasional complication for systematists. Rungwecebus, for instance, may be a taxon with a hybrid origin – a far cry from the classical assumption that hybrids between ‘true’ species will tend to be either inviable or infertile. This study systematically categorises and investigates instances of hybridisation in the Platyrrhini, whose histories have been understudied to date through a systematic review of the primatological literature, and extracts and summarises information on species involved, context (wild or captive) and outcomes to explore their potential for evolutionary impact. We use this data to investigate the hypothesis that reticulation has played an important role in platyrrhine evolution, and explore the implications for these species’ conservation.