The earliest surviving handbook of logic in Greek, the Institutio Logica was written in the second century CE by the famous Greek physician, Galen. This two-volume edition presents the Greek text with a new English translation and extensive commentary.Volume I contains the Greek text with facing translation, preceded by an extensive editors' introduction. The text is based on a reappraisal of the one surviving medieval manuscript (Parisinus Supplément Grec 635), and the introduction discusses why a doctor such as Galen is writing about logic in the first place, lays out the logical theories contained in the work, considers the authenticity of the work, and explains the principles which guide the new edition. The appendix presents a new text and translation of the short and anonymous essay On all the Kinds of Syllogism, which offers unique testimony to Galen's theory of compound syllogisms.Volume II contains a detailed and comprehensive commentary on the philosophical, historical, and textual questions raised by the text. It covers Galen's presentation of the different kinds of proposition, and his three kinds of syllogism: the hypothetical, the predicative, and the relational. The commentary explains how Galen's predicative and hypothetical syllogistic are related to but different from Aristotelian and Stoic logic, and it offers a new account of Galen's extraordinary innovation, relational syllogisms. A commentary on On all the Kinds of Syllogism offers a speculative reconstruction of Galen's theory of compound predicative syllogisms.