Social neuroscience is an emerging interdisciplinary field that combines tools from cognitive, cellular, and molecular neuroscience to understand the neural mechanisms underlying human interactions, emphasizing the complementary nature of different organization levels in the social and biological domains. Previous studies focused on the molecular/neuronal substrates of a variety of complex behaviors, such as parental behavior and pair bonding. Less is known about the various factors influencing interindividual differences in reward processing and decision making in social contexts, both relying upon the dopaminergic system. 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. Recent research combining molecular genetics, endocrinology, and neuroimaging demonstrated that variations in dopamine-related genes and in hormone levels affect the physiological properties of the dopaminergic system in nonhuman primates and 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. Taken together, the reviewed data start to unveil the relationships between genes, hormones, and the 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.