Alexander of Aphrodisias's commentary (about AD 200) is the earliest extant commentary on Aristotle's Metaphysics and the most important indirect witness to the Metaphysics text. In this study, Mirjam Kotwick demonstrates how to reconstruct from Alexander's commentary the Metaphysics text Alexander used and how to make use of this ancient version of the Metaphysics for improving the text of our direct manuscript tradition. Moreover, Kotwick investigates how Alexander's commentary may have influenced the transmission of the Metaphysics at various stages. Kotwick's study is the first book-length examination of a commentary as a witness to an ancient philosophical text. This blend of textual criticism and philosophical analysis both expands on existing methodologies in classical scholarship and develops new ones.