Mammals have developed patterns of social relationships that enhance the survival of individuals and maximize the reproductive success of species. Although social stimuli and social responses are highly complex, recent studies are providing substantial insights into their neural substrates. Neural pathways employing the nonapeptides vasopressin and oxytocin play a particularly prominent role both in social recognition and the expression of appropriate social responses. New insights into social neuroscience are discussed, along with the relevance of this rapidly developing field to human relationships and disease processes.