Since the middle Byzantine period, one of the most widely read texts on the Jesus Prayer was a lengthy letter said to be written by St John Chrysostom. The letter assumed increasing authority in the late Byzantine period when it was cited approvingly by the Synodical Tome of 1341, which championed the theology of St Gregory Palamas. The letter remained canonical reading through the eighteenth century, when it was mentioned by St Nikodemos in his prologue to the Philokalia. This book studies the history of this letter and its authorship, and presents the original Greek text together with a facing-page English translation. The book concludes with an additional work on the Jesus Prayer by St Mark of Ephesus.