Aristotle's Nicomachean Ethics is the text which had the single greatest influence on Aquinas's ethical writings, and the historical and philosophical value of Aquinas's appropriation of this text provokes lively debate. In this volume of new essays, thirteen distinguished scholars explore how Aquinas receives, expands on, and transforms Aristotle's insights about the attainability of happiness, the scope of moral virtue, the foundation of morality, and the nature of pleasure. They examine Aquinas's commentary on the Ethics and his theological writings, above all the Summa theologiae. Their essays show Aquinas to be a highly perceptive interpreter, but one who also who also brings certain presuppositions to the Ethics and alters key Aristotelian notions for his own purposes. The result is a rich and nuanced picture of Aquinas's relation to Aristotle that will be of interest to readers in moral philosophy, Aquinas studies, the history of theology, and the history of philosophy.