The paschal controversy arose from a question which, at first sight, seems to be of minor importance: the correct way of determining the date of Easter. Yet it was the most important dispute in the Irish Church until it was finally resolved in 716: most significantly, it divided the Irish Church into two opposing camps, the ‘Romans’ and the ‘Irish’ or ‘Hibernian’ party, governed by separate synods. There were, also, further consequences: the claims put forward by Kildare and Armagh that they were the sees of archbishops were largely stimulated by the dispute; it helped to sour relations between Columbanus and the Frankish episcopate; it hampered the progress of the Irish mission to the English, and, f or a time, even the Irish mission to the Picts. To understand why the paschal controversy could be of such importance for Irish churchmen, as well as for men of other nations concerned with the Irish Church (such as Athala, abbot of Bobbio, Eustasius, abbot of Luxeuil, or the Englishmen, Wilfrid and Bede), it is necessary, first, to have a rough understanding of how the date of Easter was fixed; secondly, to grasp the significance of the feast of Easter in the theology of the time; and, thirdly, to see how secondary issues became inextricably entangled with the primary issue.