M.A. (English) / The treatise on horses that forms the basis of this study is a composite text found in a 15th century manuscript previously owned by HRH Duke of Gloucester (MS G). Although sections of this text have been partially edited from other witnesses, it has hitherto been unedited from this witness. This study offers a critical edition of this treatise, including a semi-diplomatic transcription of the text, the edited text together with a textual apparatus, textual commentary and a glossary. The purpose of this study is to provide a transparent reflection of the process of editing this text. The introduction includes an overview of the relevant components and history of the text, other witnesses, previous studies and relevant theory and text-editing practices. The semi-diplomatic transcription is provided to offer the reader a point of reference, which may be used to check against the conservative critical edition and the textual apparatus. The textual apparatus provides information on textual issues and changes within the text, as well as observations concerning the features of the manuscript as deducible from the microfilm copy. The textual commentary elaborates on unfamiliar or problematic phrases and terms, and reflects on how these terms were interpreted. The glossary is selective, and includes technical or uncommon terms, along with words and phrases with unusual spellings or forms. Although this study is by no means exhaustive, the aim of this dissertation is to deal with the text as it appears in MS G, in the manner and for the purposes stated above. Since this manuscript is now in an unknown, private collection, this study will also allow for further work to be done regarding this text.