A large part of our daily lives involves interpreting other people’s behavior in terms of their underlying mental states. In particular, the capacity to recognize that others may hold and act on false beliefs plays a vital role in social interactions. According to the social-acting hypothesis, false-belief understanding represents an evolved adaptation that facilitates cooperation and in-group positivity by allowing us to distinguish between what we feel internally and what we convey to others. In this talk, I will present three recent findings that support this hypothesis: (1) false-belief belief is universally present early in development, (2) infants demonstrate a robust understanding of deceptive intent, and (3) infants understand the affective consequences of beliefs. I will also discuss ongoing projects that explore how cultural factors might give rise to individual variation in the use of this ability.