Peter Furlong presents the first systematic study of Thomas Aquinas’s account of moral responsibility. Aquinas on Moral Responsibility explores how Aquinas understands what it means to be morally responsible. Rather than focusing narrowly on freedom of the will alone, Furlong reconstructs Aquinas’s view by examining the practices through which we hold each other responsible, such as praise and blame or reward and punishment. These practices, he argues, are central to understanding what it means to be morally responsible in light of one’s actions. The book opens by clarifying Aquinas’s conception of moral responsibility itself before asking what sort of control must someone possess over their actions in order to be responsible for them. Furlong argues that Aquinas adopts a version of the Principle of Alternative Possibilities, in which agents are responsible for their actions only if they could have done otherwise. He also defends an incompatibilist interpretation of Aquinas, arguing that moral responsibility is incompatible with determinism. Furlong considers, through Aquinas, the ways in which a theory of moral responsibility must take into account ignorance, our settled character, luck, and passions. The result is a unified and carefully argued interpretation of Aquinas’s enduring contributions to debates about freedom and moral responsibility.