This volume presents the first edition of Glasgow, University Library, MS Hunter 509 (ff. 1r-167v), an English medical manuscript of the late Middle Ages. Copied in the second half of the fifteenth century, the larger part of the codex contains a witness of the Middle English Gilbertus Anglicus - a vernacular version of the Latin work Compendium medicinae, compiled by Gilbertus Anglicus ca. 1240. Its translation into Middle English is a representative document of the importance of the English language as a vehicle to transmit scientific knowledge. The number of extant copies (more than fifteen) is also proof of the significance of the text; however, most of these copies remain virtually unexplored. The manuscript also houses further treatises on humoural theory and uroscopy. All the texts comprised in MS Hunter 509 are labelled under the name System of Physic. The present edition, including an introduction, critical apparatus, notes, and glossary, aims to provide a reliable text of this medical compendium, which can be of use for research in historical linguistics, ecdotics, or the history of medicine.