In this chapter I develop the general idea that a primary function of emotions is to disambiguate social situations by providing relevant information to other individuals in the social environment. I discuss theorizing on the evolution and social functions of emotions, research on social referencing in humans and emotional understanding in non-human primates, claims regarding the universality of emotional expressions, and evidence for the deliberate targeting of emotional expressions to other individuals and for the modulation of emotional expressivity by the presence of others. I then review illustrative research on the role of emotional expressions as cues to social predispositions. The chapter closes with a brief discussion of psychological disorders and physical conditions that compromise social interaction by disrupting the social-communicative functions of emotions.