Giles Constable presents the first critical edition of the letters of Peter the Venerable, abbot of Cluny from 1122 to 1156, to appear since the first printed edition was published in 1522. The text, based upon a comparison of all known manuscripts, is printed in Volume I and is an important source for the history of the first half of the twelfth century. An introduction, appendices, and notes which touch broadly upon the ecclesiastical, intellectual, and political history of the period are provided in Volume II.