Sin is clearly evil, but what differentiates sin from evil? The idea that sin is moral evil is widely held, but important theological arguments have been posed against it. Theologians who reject sin moralism have, however, found it hard to distinguish sin from evil—partially because they share hidden assumptions with sin moralists. Helped by a philosophical theology of deep responsibility, I propound sin responsibilism: sin is culpable evil. This analysis of sin is open to multiple accounts of sin's relation to morality or theories of responsibility, and thus of sin's scope—but I defend a non-moralistic, compatibilist sin responsibilism.