THE process which saw the foundation of the great medieval English Benedictine monasteries in the tenth century was, if not necessarily the most important development within the English church of the time, certainly the best recorded. Many aspects of the process – including the use of the term ‘reform’ – have been undergoing re-evaluation recently. However, mapping out the chronology of the Benedictine movement overall has not been attempted since David Farmer sketched it out in the early 1970s, summarising the account in David Knowles' Monastic Order, so it is high time to re-attempt it. Chronology matters because establishing the sequence of events is a necessary step before working out causation and influence. It also allows us to observe which group of people was operating in any particular context. This paper will deal with the chronology of the Benedictine movement in Edgar's reign not only because Edgar is the subject of the volume, but also because his reign was the most dynamic period of the process. Part of the key to working out the chronology of the Benedictine movement under Edgar is the identification of a satisfactory date for Regularis Concordia, the set of uniform monastic customs commissioned by Edgar and written by Æthelwold of Winchester to be followed by all inmates of Benedictine communities in England. Regularis Concordia became necessary once there were several houses in existence following slightly different variations of the Benedictine routine, which Edgar viewed as a worrying development. He wished to impose a unified observance on all monks and nuns in his kingdom.