This collection of documents represents the surviving output of the clerks of what became the most powerful magnate dynasty in England, Wales, and Ireland in the thirteenth century. Its greatness did not last even half of that century, however: the Marshal earls were powerful at court and in the various Angevin realms in Britain and France only from 1190 to 1245. But as a result of the Marshals' spread of interests and marriage alliances the charters and letters edited here embrace a remarkable diversity of lordships and societies. That fact and the central place the two Earls William Marshal held at the court of the young Henry III between 1216 and 1231 give this collection a particular interest for medieval historians of Britain and France, more so perhaps than for any other contemporary magnate family.