Amongst the manuscripts bequeathed to Corpus Christi College, Cambridge, by Matthew Parker in 1575 is one of the most important surviving collections of sources for the history of the north of England in the twelfth century. Manuscript 139, as it now is, contains, amongst other items, unique, or almost unique, copies of the so-called Historia Regum, which had been ascribed to Symeon of Durham before the end of the twelfth century, its continuation by John of Hexham, and the History of Richard of Hexham. It was a prime, and in part a unique, source of Twysden’s pioneering edition of 1652, and its value is in no way diminished today. This apart, the manuscript is of great interest as a manuscript, and the problems of its date, provenance and composition are still the subject of debate. The most recent and definitive account of the manuscript was given by Peter Hunter Blair in a fifty-five page article contributed to the volume of essays edited by Nora Chadwick under the title Celt and Saxon. His conclusions, which supersede all earlier views, were that the manuscript was compiled in the period c 1165–70 at the cistercian house of Sawley in the West Riding of Yorkshire, and the subsequent discovery of an erased Sawley ex libris, now visible only in ultra-violet light, and dated by Ker to the late twelfth/early thirteenth century, reinforced his view. Yet there still remain problems and uncertainties, and my purpose here is first to sketch in a little of the history of the manuscript in its present form, and secondly, by further examination of particular aspects of its to supplement and qualify Blair’s conclusions.