Hormonal and chemosensory signals regulate social behaviors in a wide variety of mammals. In the male Syrian hamster, these signals are integrated in nuclei of the medial extended amygdala, where olfactory and vomeronasal system transmission is modulated by populations of androgen- and estrogen-sensitive neurons. Evidence from behavioral changes following lesions and from immediate early gene expression supports the hypothesis that the medial extended amygdala and medial preoptic area belong to a circuit that functions selectively in male sexual behavior. However, accumulated behavioral, neuroanatomical, and neuroendocrine data in hamsters, other rodents, and other mammals indicate that this circuit is embedded in a larger integrated network that controls not only male mating behavior, but female sexual behavior, parental behavior, and various forms of aggression. In this context, perhaps an individual animal's social responses can be more easily understood as a repertoire of closely interrelated, hormone-regulated behaviors, shaped by development and experience and modulated acutely by the environmental signals and the hormonal milieu of the brain.