Aquinas's views about the morality of lying are well known and often discussed by commentators. But his views about the nature of lying have yet to receive the attention they deserve. In this article, I take some of the first steps necessary to correct this state of affairs by clarifying and offering a limited defense of the account of lying that Aquinas presents in in his Summa Theologiae—more specifically, in that portion of it known as the treatise on truth (Part 2-2, Questions 109–113).