This volume deals with books II and III of On The Doctrines of Hippocrates and Plato , by the medical scientist and philosopher, Galen of Pergamum (129-210 AD). In these books Galen offers a critique of Stoic psychology, quoting a large number of passages from the otherwise lost treatise On the Soul by the Stoic philosopher, Chrysippus. This study of Chrysippus’s mode of argumentation considers the fragments both in their Galenic context and in relation to Stoicism in general. A separate discussion is devoted to Galen’s aims and methods, and the traditions to which he is indebted. Though designed as a foil for the treatment of Chrysippus, this text should also be of interest to those interested in Galen’s methodology for its own sake.