In classical Latin rhetoric, the related terms affectio and affectus have a wide presence. 1 Of course, any rhetorical use of those terms is inflected by their broader semantic values in Latin antiquity. But restricting our survey to the narrowed optique of rhetorical contexts produces a suggestive picture. In the rhetoric of the postclassical periods up to about 1200, these terms tend to have a value limited by one of the chief rhetorical sources that the Middle Ages took from classical antiquity, Cicero’s youthful De inventione. While Latin antiquity produced rhetorical works of much greater scope and depth, mere accidents of history made De inventione the most influential rhetorical text to survive from Late Antiquity through the High Middle Ages. This work offers a definition of affectio as commutatio animi, a disturbance of the mind (or soul). Here, Cicero accords affectio some theoretical value as one among various resources for inventing or ‘discovering’ an argument about a person. For almost the next 1,000 years, rhetorical attention to this principle usually reflects the constraints that Cicero’s Stoic thought placed on it. In the short compass of this chapter I will consider the use of affectio in De inventione, with briefer attention to Cicero’s mature rhetoric and the work of Quintilian, and then turn to the rhetorics of Late Antiquity to see how affectio-affectus established themselves in that body of work. I end the chapter by considering how the terms figure in Ciceronian commentary and pragmatic rhetorics from the late eleventh to the late twelfth centuries, the period that sees the most significant new assimilations of Cicero’s rhetorical thought. 2