A well-mapped set of brain regions is dedicated to social cognition. It is responsive to social cues, engaged in moral decision-making and makes predictions about the likely behaviour of other people. Recent studies of affiliation, using animal models, have revealed that specific neurotransmitters and hormones influence the neural circuits of 'the social brain'. There is converging evidence that the interface between the neuropeptides oxytocin and vasopressin and dopaminergic reward circuits is of particular importance. In the context of recent research, we discuss emerging evidence for the impact of these neuropeptides on the regulation of the social brain. We also examine the putative role of allelic variation in candidate genes on individual differences in social cognitive processing and associated social behaviour.