By the end of the twelfth century, Matilda de Bailleul, abbess of Wherwell Abbey in Hampshire, England (c. 1174–1212), had acquired a finely decorated psalter for her personal use, now Cambridge, St John’s College, MS C.18 (68). The book still bears signs of her ownership – entries of her relatives’ obits in the opening calendar and additions of prayers tailored for an abbess – and the marks of its subsequent owners, her abbatial successors, over the course of the thirteenth century. Scholars of the psalter are in agreement that an artist and two scribes affiliated with, but likely not members of, St Albans Abbey in Hertfordshire were responsible for the psalter’s initial production. But their consensus divides over the questions of who originally commissioned and owned the psalter, and how the book then came into Matilda’s possession. This seminar presentation will answer both questions, drawing on liturgical evidence internal to the psalter itself and on charters and narrative sources attesting to the lives of Matilda and her relatives. Ultimately this presentation will make a case for identifying Matilda’s maternal uncle, Osto of Saint-Omer (d. c. 1174), a Templar based first in Flanders, then in England, as the psalter’s original recipient.