This critical edition presents the trilingual glossary in London, British Library, Manuscript Harley 219, which was produced by Thomas Hoccleve and bound into a manuscript that stayed in London bureaucratic circles after his death. Hoccleve's glossary uniquely combines a variety of sources in innovative ways and demonstrates his approaches to glossary organization and second-language reference materials. This volume situates Hoccleve's glossary within multiple relevant contexts: late medieval glossaries and French language-learning texts, literary texts in Harley 219, and Hoccleve’s career at the Royal Office of the Privy Seal and as a Middle English poet. The trilingual glossary contributes to studies of the French of England and the manuals that reinforced knowledge of the language among London and Westminster clerks. It provides new evidence of these clerks' multilingualism that goes beyond the legal and practical purposes necessary for their professional careers.