Marsilius of Inghen's Sentences Commentary is a crucial piece of evidence in the history of thought between Ockham and Luther, covering almost the complete range of items important in pre-modern philosophy and theology. The part edited here is concerned with the Trinity, dealing with the unity and the distinction of the divine persons. It addresses the use of logic in theology, the dialectics between authority and reason, and reveals new evidence on the debates between Realists and Nominalists at the Universities of Paris and Heidelberg. The present edition provides the reader a first critical text based on an assessment of all textual witnesses, thus offering an indispensable tool for uncovering the intricacies of Scholasticism at the eve of Reformation.