Libertarianism about free will is the view that we have free will, and that our having it is incompatible with causal determinism. This view that is sometimes held to underpin moral and criminal responsibility, as well as retributive punishment. In its contemporary forms, it is standardly presented as compatible with a broadly scientific picture of the world. This paper argues that there is good reason—grounded in empirical data—to think that libertarianism about free will is not a product of disinterested reasoning about the requirements of free will, responsibility, or retributive punishment. Instead, both empirical and conceptual considerations suggest that libertarianism is largely a product of motivated reasoning by theists, i.e., believers in the existence of God. This essay develops the case for that conclusion, and considers its consequences.