A functioning democracy relies on social interactions between people who disagree—including listening to others’ viewpoints, having political discussions, and finding political compromise. Yet social life in the contemporary United States is characterized by a relative lack of interaction between Democrats and Republicans (or, social polarization). We argue that political anger contributes to social polarization by causing Americans to cut off ties with opposing partisans. We first draw on data from the American National Election Studies and the Wesleyan Media Project to show that the mass public is increasingly angry and that politicians often seek to elicit anger. We then present results from a survey experiment on nearly 3,500 Americans, finding that the exogenous introduction of anger leads partisans to socially polarize across a range of settings. Our findings suggest that increasing levels of political anger paralyze politics and harm democracy by influencing Americans’ social interactions and relationships.