A set of thirteenth-century parchment fragments, including the remnants of two rolls and one manuscript codex, preserves a largely unstudied repertoire unique to medieval England. In addition to a single motet and a setting of a responsory verse, the Rawlinson Fragments preserve twelve three-voice Alleluya settings. While polyphonic Alleluyas are well known from the continental Magnus liber repertoire, these insular Alleluya settings are quite different. Most significantly, while composed on the text and pitches of plainchant, they include newly composed texts in at least one voice—that is, they are polytextual chant settings. Aspects of their musical style certainly draw on other polyphonic genres—organum, conductus, and motet. This article presents the paleographical and codicological evidence that corroborates an early date for these fragments (in the 1240s), confirms their connection to Reading Abbey, and situates their repertoire within a broader context. My analysis points to intriguing points of overlap with both the plainchant prosula tradition and the Magnus liber organa and motets. It reopens broader questions about the copying and performance practices of liturgical polyphony, including previous suggestions that motet texts may have been sung within the performance of the Magnus liber organa, regardless of the scribal copying conventions that separated organum and motet in the surviving Magnus liber manuscripts. The article also considers the role of the Rawlinson Fragments’ main scribe, Benedictine monk W. de Wicumbe, who was active within the monastic communities of Leominster and Reading as a composer of plainchant and polyphony, and as precentor, most likely in charge of his community's musical life.