Researchers have struggled to obtain a clear account of the evolution of prosocial behaviour despite a great deal of recent effort. The aim of this review is to take a brief step back from addressing the question of evolutionary origins of prosocial behaviour in order to identify contextual factors that are contributing to variation in the expression of prosocial behaviour and hindering progress towards identifying phylogenetic patterns. Most available data come from the Primate Order, and the choice of contextual factors to consider was informed by theory and practice, including the nature of the relationship between the potential donor and recipient, the communicative behaviour of the recipients, and features of the prosocial task including whether rewards are visible and whether the prosocial choice creates an inequity between actors. Conclusions are drawn about the facilitating or inhibiting impact of each of these factors on the expression of prosocial behaviour, and areas for future research are highlighted. Acknowledging the impact of these contextual features on the expression of prosocial behaviours should stimulate new research into the proximate mechanisms that drive these effects, yield experimental designs that better control for potential influences on prosocial expression, and ultimately allow progress towards reconstructing the evolutionary origins of prosocial behaviour.