Richard Rolle, the Yorkshire hermit and scholar (d. 1349) wrote two commentaries on the Psalms, one in Latin and one in English. Some fifty years after he died, his English commentary was revised by a series of Lollard writers, and this redaction was itself subsequently modified by other revisers, having a similar radical outlook. This edition presents for the first time a full edition of the first of the Lollard revision, and gives detailed evidence for the second. It is based on a full study of all manuscripts of both versions, and includes the commentaries on the twelve Canticles which accompanied the Psalter commentary, and seem to have been regarded as a part of the whole. This first Lollard revision reveals the work of a complex organisation: an academic team which worked on the text for a considerable time, and whose work was not in every respect complete. This is the first of a three-volume edition. Volume 1 contains the Introduction and Psalms 1-34; the remaining two volumes (to appear as O.S. 341 and 343) will contain the remainder of the text, Explanatory Notes, and Glossary.