A world without free will is an amoral world. Belief in free will is a pervasive phenomenon that has important consequences for prosocial actions and punitive judgments, but little research has investigated why free will beliefs are so widespread and what function they serve. Across ten studies using experimental, survey, and archival data, and multiple measures of free will belief, I tested the hypothesis that a key factor promoting belief in free will is a fundamental desire to hold others morally responsible for their wrongful behaviors. In Study 1, participants rated morally bad historic figures as having had more freedom of choice in their lives than morally good historic figures. Study 2 found that considering others' immoral actions, though not one's own, increased attributions of free will to the actor. In Study 3, participants reported greater belief in free will after considering an immoral action than a morally neutral one, thus showing that this effect extended beyond actor-specific attributions to generalized beliefs about the human capacity for free will. Study 4 showed that this effect was limited to actions that victimize morally good people. Study 5 demonstrated the effect with an indirect measure of free will belief by showing that reading about others' immoral behaviors reduced the perceived merit of anti-free will research. I also found converging evidence linking the free will beliefs of entire national populations with their crime and homicide rates (Study 6). Study 7 provided evidence that this effect was due to heightened punitive motivations. In a field experiment (Study 8), an ostensibly real classroom cheating incident led to increased free will beliefs, again due to heightened punitive motives. Thus, free will belief, which has traditionally been considered a stable worldview, appears to be situationally motivated. Two additional studies demonstrated correlationally (Study 9) and experimentally (Study 10) that heightened belief in free will alleviated the negative psychological consequences associated with punitiveness. Taken together, my findings suggest that the strength and resilience of free will beliefs reflect a general desire to invest the world with moral significance - to hold people morally responsible by seeing them as having choice.