 Iamblichus wrote an extensive commentary on the Categories, fragments of which have been preserved by Simplicius and Dexippus (a student of Iamblichus): in addition to literal quotes, Iamblichus is behind much of Simplicius’ extant exegesis of this treatise. We also have evidence that Iamblichus wrote a commentary on Aristotle’s Prior Analytics and we know about his exegetical work on the De interpretatione and the De caelo (see Opsomer 2015). From the first century BC onwards, Platonist philosophers had been familiar with Aristotle’s Categories: Platonists such as Eudorus of Alexandria and Nicostratus raised objections against Aristotle’s doctrine; Plotinus wrote a very important treatise On the Genera of Being, where he critically discussed Aristotle’s categories (Ennead VI, 1–3). To the best of our knowledge, however, no Platonist wrote a commentary on Aristotle’s Categories before Porphyry, who was the author of two commentaries on this treatise: a short and extant elucidation in a question-and-answer format and a very extensive commentary in seven books dedicated to someone called Gedalius, which is now lost. In addition, Porphyry wrote an introduction to logic, the Isagoge, which is closely connected to the Categories. With Porphyry, then, Aristotle’s Categories became an integral part of the Platonist curriculum and this was a crucial move for the subsequent history of Late Antique and medieval philosophy. As is often the case, Iamblichus’ exegetical work relies on Porphyry but introduces some changes which are probably aimed to supplement (and possibly supplant) Porphyry’s approach. Simplicius informs us that Iamblichus followed the great and now lost commentary written by Porphyry, while adding two distinctive features. First Iamblichus “applied his Intellective Theory (noera theōria) everywhere, to almost all of the chapter-headings” (Simplicius, In Categorias, 2.13–15 [DL-1972: Fr. 2], trans. Chase; see Dillon 1997). Iamblichus employs the same expression, noera theōria in the opening section of the Reply to Porphyry (I, 2 [SS-2013: 4.16]), in a passage where he characterizes the mode of inquiry that is typical of theology. Secondly, Iamblichus took Archytas’ treatise On the All to be Aristotle’s source and he developed a thoroughly Pythagorising interpretation of the Categories (Simplicius, In Categorias, 2.15–25 [DL-1972: Fr. 2]; see Hoffmann 1980). Archytas’ treatise is actually a forgery which scholars now date to the first century BC. Iamblichus, however, took it to be a genuine work by Archytas and in doing so he claimed a Pythagorean origin for Aristotle’s theory. To sum up, Iamblichus’ exegesis of the Categories was an integral part of his Pythagorean philosophical programme and in interpreting the Categories Iamblichus made use of his metaphysical and theological views. Apparently, Iamblichus pushed his reading of Aristotle along Platonic/Pythagorean lines so far that (as later sources report) he did not refrain from assuming that Aristotle was not opposed to Plato on the theory of Ideas (see Elias/David, In Categorias, 123.2–3).