This volume provides a comprehensive history of the martyrological transmission of the feastdays of the Irish saints, from its beginnings on Iona in the early 8th century, in a text probably brought from Lindisfarne in Northumbria, to its completion in the late 1620s in the humble refuge of the Donegal Franciscan friary. The route followed by the Iona text, first to Bangor in Ulster, then to Tallaght near Dublin, is explored in several chapters by reference to the feasts added along the way. The metrical version, produced at Tallaght about 830 by a bishop named Óengus, is shown to have been the most popular of all, with numerous copies, including one, now lost, which reached Regensburg in the late 11th century. The circulation in Ireland of the martyrologies of Ado and Usuard, on which the later Roman Martyrology is based, is also examined. One of these, formerly kept at Christ Church cathedral, is arguably Dublin ‘s oldest known book. The volume is accompanied by a full critical apparatus, with bibliography, map, and several indexes.