Commentary was an important vehicle for philosophical debate in late antiquity. Its antecedents lie in the rise of rational argumentation, polemical rivalry, literacy, and the canonization of texts. This essay aims to give a historical and typological outline of philosophical exegesis in antiquity, from the earliest allegorizing readings of Homer to the full-blown "running commentary" in the Platonic tradition (fourth to sixth centuries CE). Running commentaries are mostly on authoritative thinkers such as Plato and Aristotle. Yet they are never mere scholarly enterprises but, rather, springboards for syncretistic clarification, elaboration, and creative interpretation. Two case studies (Galen 129-219 CE, Simplicius ca. 530 CE) will illustrate the range of exegetical tools available at the end of a long tradition in medical science and in reading Aristotle through Neoplatonic eyes, respectively.