The writings of Siger of Courtrai were first edited by Gaston Wallerand in 1913. This new edition on the basis of Wallerand's editio prima , with additions, critical notes, and an introduction by Jan Pinborg, reprints the two works from that edition that have an immediate relevance for the study of medieval grammar, i.e., the Summa modorum significandi, and the Sophismata. To this have been added some critical notes, correcting the text of Wallerand where his readings were faulty, and supplying references of the sources. Finally, three more Sophismata which have recently been recovered are here edited for the first time.The Summa is a compendium which closely follows Priscian's Institutiones, but puts the doctrinal elements from Priscian into the frame of reference characteristic of Modistic literature. The importance of Siger's Sophismata in the context of this volume is that they offer a more thorough discussion of the fundamental logico-epistemological tenets presupposed in his linguistic theory.