From the first century BCE onwards, philosophers started to write commentaries on those Aristotle’s treatises that were meant for the internal use of his school. Plato’s works had been commented on already earlier, the first reported commentary originates in the 300s BCE. Commentaries are treatises that follow an object text in a more or less linear fashion. The format was not unknown before the first century BCE but new in extensive philosophical use. This review essay focuses on authors who commented (...) on Aristotle’s works. The commentaries emerged when Platonists and Aristotelians observed the need to teach the philosophy of these ancient masters to their students and to systematise their philosophy to respond to rival schools. In the late ancient schools, Plato and Aristotle were considered great thinkers, whose views needed to be studied carefully when considering any matter at hand. Many also argued that, despite the initial appearance to the contrary, there is no deep disagreement between Plato and Aristotle but, rather, a division of labour; Aristotle is dominant in natural philosophy and Plato in theology. However, this harmony thesis was not universally accepted. Despite their respect for Plato and Aristotle, the commentators were not mere followers of these authors. They developed, criticised and transformed the doctrines in significant ways, not only by suggesting different answers to the same questions but also by transforming the questions themselves. (shrink)