Central to the teachings of Christianity is a puzzle: on the one hand, sin seems something that humans do not do freely and so cannot be not responsible for, since it is unavoidable; on the other hand, sin seems something that we must be responsible for and so do freely, since we are enjoined to repent of it, and since it makes us liable to divine condemnation and forgiveness.After laying out the puzzle in more depth, this Element considers three possible responses—libertarian, soft determinist, and free-will skeptic—and weighs the costs and benefits of each.