Social neuroscience is an emerging interdisciplinary field combining tools from cognitive, cellular and molecular neuroscience to understand the mechanisms underlying human social interactions, emphasizing the complementary nature of different organization levels in the social and biological domains. Previous studies focused on the study of the molecular/neuronal substrates of a variety of complex behaviors, such as parental behavior and pair bonding. Less is known about the different factors influencing intra- and inter-individual differences in reward processing and decision-making in social contexts, both relying upon the dopaminergic system. Recent research combining molecular genetics, endocrinology and neuroimaging tested whether intra- and inter-individual differences in dopaminergic transmission involve changes in reward processing and social interaction. Variations in dopamine-related genes and in hormone levels have been shown to affect the physiological properties of the dopaminergic system in non-human animals and to modulate the processing of reward and social information in humans. These findings are important because they indicate the neural influence of genes conferring vulnerability to develop neuropathologies such as drug addiction and pathological gambling. This review concerns: (1) basic electrophysiological findings and recent neuroimaging findings showing that reward processing and social interaction processes share common neural substrates, and (2) genetic and hormonal influences on these processes. Taken together, the reviewed data start to unveil the relationships between genes, hormones and functioning of the reward system as well as decision making in social contexts and provide a link between molecular, cellular and social cognitive levels in humans.