The present volume contains a critical edition and an English translation of Testa nucis and Poetria, both texts written by the Swedish 14th-century theologian Magister Mathias Lincopensis. Compared to the edition published by S. Sawicki in 1936, the present work offers another text in c. 140 passages, many of which directly affect the understanding of the text. Whereas the Testa nucis, 'The Nutshell' (preserved only in a fragment), represents traditional rhetorical doctrine, the Poetria is remarkable in that Mathias seems to be the first, and for a long time the only, medieval Latin writer to try to integrate Aristotelian theory in a treatise on poetry. This and related questions are discussed in the introductory chapter, and problems of critical and exegetic nature are dealt with in another. Two indices conclude the edition.