This chapter investigates the Treatise on the Passions of the thirteenth-century theologian, Thomas Aquinas and, specifically, his treatment of the role of emotions in the moral life. After clarifying language and offering a working definition of an emotion, the chapter unfolds in seven stages. First, it investigates Aquinas’ understanding of an emotion as a psychological and bodily reality. Second, the categories of emotions (and their philosophical underpinnings) used by Aquinas are explained. This leads, third, to a working blueprint for the moral status of emotions and the role of emotional and bodily resonance. Fourth, since, for Aquinas, the moral function of emotions rests on his understanding of the affective (moral) virtues, one must consider their necessity, location, and immanence. Importantly, the terminus specific to affective virtues (viz., fortitude and temperance) is not primarily action but appropriate emotional response. Aquinas examines emotions as moral and voluntary together with their relationship to required attitudes and dispositions (character) integral to moral reasoning and a good moral life. This leads to outlining a contemporary approach to traditional cardinal virtues. Fifth, we consider the controlling metaphor (the polis) used by Aquinas to capture the interdependence and mutual collaboration of emotions, intellect, and will. Sixth, attention is given to Aquinas’ insights into the negative emotions and their disturbing, even, destructive aspects. The chapter closes with some brief comparative and evaluative comments and how Aquinas transcended the limits of his philosophical framework while intimating the scope of his moral imagination and moral sensibility.