I will describe research showing that the social decisions we make (ranging from judgments of facial expressions to decisions about how to allocate resources in an economic game) are shaped by a combination of others’ behaviour and the emotions they express. I will argue that the process underlying this social influence is one of social appraisal: our appraisals of the world around us are shaped by the way in which others appraise it, and their appraisals are inferred from their emotional expressions. Knowledge of others’ appraisals is especially likely to influence judgments about ambiguous stimuli and decisions that involve competition between selfish and prosocial norms. Emotions therefore serve an important interpersonal function by shaping other people’s social decisions.