This thesis will examine the iconography of late-thirteenth- through fifteenth-century images of St. Veronica's veil, also known as vernicles. In the late Middle Ages, vernicle iconography changed from iconic representations of Christ's face toward graphic imagery of Christ's suffering during his Passion. These passionate transformations, as I have called them, were affected by the Roman Sudarium relic, popular devotion to Christ's suffering and humanity during his Passion, and the Catholic ritual of Mass. This thesis will consider how the function of vernicle images during Mass was reflected in their iconography throughout Europe between 1250 and 1500.