CCCC MS 266 contains Letters 1127, 1315, 1378, 143 of Peter of Blois (d. 1212), and was written in the thirteenth century. It has been designated as one of the manuscripts of the second edition which should be used as a basis for any future critical edition. Some of these letters are of major significance in regard to the controversy between Henry II and Thomas Becket. The MS also includes several other minor works of Peter of Blois, some of which commonly circulated with his Letters. The manuscript contains the distinctive pressmark of the London Carmelites.