A popular thesis in psychology holds that ordinary people judge others’ mental states to be uncontrollable, unintentional, or otherwise involuntary. The present research challenges this thesis and documents how attributions of mental state control affect social decision making, predict policy preferences, and fuel conflict in close relationships. In Chapter 1, I show that lay people by-and-large attribute intentional control to others over their mental states. Additionally, I provide causal evidence that these attributions of control predict judgments of responsibility as well as decisions to confront and reprimand someone for having an objectionable attitude. By overturning a common misconception about how people evaluate mental states, these findings help resolve a long-standing debate about the lay concept of moral responsibility. In Chapter 2, I extend these findings to interpersonal emotion regulation in order to predict how observers react to close others who experience stress, anxiety, or distress. Across six studies, I show that people’s emotional support hinges on attributions of emotion control: People are more inclined to react supportively when they judge that the target individual cannot regulate their own emotions, but react unsupportively, sometimes evincing an intention to make others feel bad for their emotions, when they judge that those others can regulate their negative emotion away themselves. People evaluate others’ emotion control based on assessments of their own emotion regulation capacity, how readily reappraised the target’s emotion is, and how rational the target is. Finally, I show that judgments of emotion control predict self-reported supportive thoughts and behaviors in close relationships as well as preferences for university policies addressing microaggressions. Lastly, in Chapter 3, I show that people believe that others have more control over their beliefs than they themselves do. This discrepancy arises because, even though people conceptualize beliefs as controllable, they tend to experience the beliefs they hold as outside their control. When reasoning about others, people fail to generalize this experience to others and instead rely on their conceptualization of belief as controllable. In light of Chapters 1 and 2, I discuss how this discrepancy may explain why ideological disagreements are so difficult to resolve.