Research suggests that people can accurately predict the political affiliations of others using only information extracted from the face. It is less clear from this research, however, what particular facial physiological processes or features communicate such information. Using a model of emotion developed in psychology that treats emotional expressivity as an individual-level trait, this article provides a theoretical account of why emotional expressivity may provide reliable signals of political orientation, and it tests the theory in four empirical studies. We find statistically significant liberal/conservative differences in self-reported emotional expressivity, in facial emotional expressivity measured physiologically, in the perceived emotional expressivity and ideology of political elites, and in an experiment that finds that more emotionally expressive faces are perceived as more liberal.