The medieval Welsh bardic grammars were composed and transmitted during a period of intense social and political change in Wales. These documents, which contain both a highly Latinate description of the Welsh language and a treatment of the strict poetic metres, began their life as essentially vernacular artes poetriae. However, from the early fourteenth century to the end of the sixteenth, they were recopied and revised over and over by bards, bureaucrats, antiquarians, humanists, and the readers and reciters of poetry. At different times they served as practical handbooks, official regulatory documents and attempts to realign the Welsh texts with contemporary Latin and English scholarship. This book weaves a close textual analysis of the revisions made to the text into a broader consideration of the historical contexts that gave rise to each subsequent version. The resulting narrative offers insight into the development of Welsh bardic and scholarly practices over the course of two centuries.