This introduction sets forth the approach to Byzantine commentaries on ancient Greek texts taken in this volume: it places the Komnenian and Palaiologan commentaries firmly within their intellectual and sociocultural contexts and examines the process of commenting on ancient texts as a deliberate and culturally significant choice made by the commentators. We define commentary both in a narrow and a broad sense. In the narrowest sense, commentaries are concerned with explaining an ancient text and the knowledge related to it, often in a didactic context. Defined more broadly, commentaries include treatises on ancient literature and paraphrases of ancient authorities, which likewise demonstrate how these texts were read and taught. In the broadest sense, commentaries can be any literary texts that creatively engage with ancient texts and thus shed light on Byzantine attitudes towards their ancient heritage. The very practice of composing commentaries on ancient texts was a creative and targeted enterprise of identity building. The introduction discusses different kinds of Byzantine commentaries on ancient poetry and prose within the context of the study and teaching of grammar, rhetoric, philosophy and science, and introduces some of the key figures of the Komnenian and Palaiologan periods.