This book offers a new edition, with English translation and commentary, of the Kitāb al-Madḫal, which opens Avicenna's (d. 1037) most comprehensive summa of Peripatetic philosophy, namely the Kitāb al-Sifāʾ. For the first time, the text is established together with a stemma codicum showing the genealogical relations among 34 manuscripts, the twelfth-century Latin translation, and the literal quotations by Avicenna's first and second-generation students. In this book, Avicenna's reappraisal of Porphyry's Isagoge is examined from both a historical and a philosophical point of view. The key-features of Avicenna's theory of predicables are analyzed in the General Introduction and in the Commentary both in their own right and against the background of the Greek and Arabic exegetical tradition. Readers shall find in this book the first systematic study of the Madḫal which, in addition to being the only logical work of the Sifāʾ ever transmitted in its entirety both in Arabic and in Latin, is crucial for understanding Avicenna's conception of universal predicables at the crossroads between logic and metaphysics.