This book provides a collection of sources, many of them fragmentary and previously scattered and hard to access, for the development of Peripatetic philosophy in the later Hellenistic period and the early Roman Empire. It also supplies the background against which the first commentator on Aristotle from whom extensive material survives, Alexander of Aphrodisias (fl. c. AD 200), developed his interpretations which continue to be influential even today. Many of the passages are here translated into English for the first time, including the whole of the summary of Peripatetic ethics attributed to 'Arius Didymus'.