The twelfth-century anonymous Glossae Doctrinae Sermonum presents a commentary on Aristotle’s Peri hermeneias that makes extensive use of Peter Abaelard’s own commentary, as well as drawing on other contemporary sources. In addition to its historical value - the author apparently made use of an earlier version of Abaelard’s commentary than we now possess - it is of philosophical interest in its own right. The author offers his own theory of true and false understandings, criticizing the theory put forward by Abaelard, and offers his own analysis of modal logic. The text is a mixed commentary since it combines careful exegesis of Aristotle with independent self-contained analyses of philosophical issues raised by Aristotle’s text. In covering the Peri hermeneias, the Glossae Doctrinae Sermonum deals with issues in philosophical semantics, the philosophy of mind, and logic in both its assertoric and modal forms. The text of Peter Abelard’s Glossae super Peri hermeneias is transmitted completely only in manuscript B. In manuscript A the scribe breaks off in the middle of the extended analysis of modal propositions, which precedes the commentary to Chapter XII. After a few empty lines there follows an independent short treatise on modalities, which certainly is not a a work of Abelard. The text shows that the theory of modal propositions was of great interest not only for Abelard, but for a wider circle of philosophers in the twelfth century as well. Extensive indices for Peter Abelard’s commentary on Peri hermeneias will support specialized studies in Abelard’s logic and semantics. They should be a help also for research on the relation between Abelard’s Dialectica and his Glossae super Peri hermeneias.