This article is concerned with paper in the medieval Gaelic law manuscript tradition during the initial phases of the paper tradition in Ireland.1 Paper was introduced into the Gaelic manuscript tradition in the late fifteenth century, but it took several centuries before it replaced vellum entirely as the preferred writing medium.2 Recent studies have highlighted the gradual change to paper from vellum in manuscripts compiled in Irish schools of learning, particularly those of medicine and history.3 The extent to which paper usage prevailed in the professional law schools during this initial phase has not yet been fully explored, however. This article provides a general survey and discussion of paper use in the vernacular Irish law manuscripts, with particular focus on the largest such collection, which is held in the Library of Trinity College Dublin. The evidence demonstrates that the professional Irish law schools were not isolated from the wider trends and practices of book production taking place in Ireland. Scribes not only adopted the new writing technology but also implemented innovative new page layouts in both materials, drawing on external influences of imported printed books, demonstrating flexibility and dexterity working between both media.