This is the first volume in over a century devoted to the second century BCE Peripatetic philosopher Critolaus of Phaselis, covering his views on cosmology, god, ethics, rhetoric and politics. Critolaus of Phaselis was the most prominent Aristotelian philosopher of the second century BCE; he was at the center of debates in ethics and rhetoric, and there is evidence that he also developed views on the nature of the soul, god and the cosmos, as well as on politics and history. Nothing that he wrote survives in full, but aspects of his doctrine are known from references in later literature. This volume explores every aspect of his work, reconstructing Critolaus' philosophical convictions and analysing his position in the context of Hellenistic philosophy, especially in relation to Stoic philosophy. Critolaus of Phaselis offers a fascinating insight into an understudied figure. The book is suitable for students and scholars of Aristotelian and Peripatetic philosophy, as well as Hellenistic philosophy more broadly.