In this chapter, we shall discuss one aspect of the cellular mechanism of action of steroid hormones on social behaviors, the role of steroid hormone receptors. Unfortunately, the study of cellular mechanisms of hormones is not compatible with many social behaviors. Therefore, the vast majority of these studies has been aimed at delineating the involvement of steroid hormone receptors on one social behavior — sexual behavior. In particular, most of these studies have focused on female sexual behavior, and most have used rats and guinea pigs as the model species. Very recently investigation has begun to extend into other social behaviors, including social play, aggressive behavior, and maternal behavior.