This is the first book-length study in English of the interpretative and philosophical approach of the commentaries of Simplicius of Cilicia (c. AD 530). Simplicius' work, marked by doctrinal complexity and scholarship, is unusually self-conscious, learned and rich in its sources. Consequently, he is one of those rare authors who is of interest to ancient philosophers, historians and classicists alike. The book argues that our understanding of Simplicius' methodology will be greatly enhanced if we study how his scholarly approach impacts on his philosophical exegesis. His commentaries are placed in their intellectual context and several case studies shed light on his critical treatment of earlier philosophers and his at times polemical use of previous commentaries. The investigation opens up connections with broader issues, such as the reception of Presocratic philosophy within the commentary tradition, the nature and purpose of his commentaries, and the demise of pagan philosophy.