In the last quarter of the eleventh century, before 1102, Daniel, a lay monk of Lérins abbey (France) wrote, at the request of his abbot (Eldebert) and for his convent, a Psalter commentary. The manuscript is lost but the text of the dedicatory letter has survived, because it was copied by dom Claude Estiennot in 1681. This copy passed on to Mabillon, who, however, did not understand its significance, and it remained unpublished. The letter shows how certain monks had difficulties in reading the Psalter, glossed "in margins and between the lines". The abbot of Lérins therefore ordered Daniel to prepare an independent written out commentary, integrating all the Gloss sentences. This letter offers a reference point that is unexpected in several respects. It helps put into perspective the history and the success which met the Gloss of Laon during the twelfth century. The style and structure of the document, edited here for the first time, are studied in parallel with the dedicatory letter of another preserved Psalter commentary, written shortly after, but in Northem Italy (Assisi, Sacro Convento, 83).