This thesis will argue that the late seventh-century ecclesiastical law, Ca?in Adomna?n, was promulgated in A.D. 697 by the ninth abbot of Iona to bolster Columban interests: the flagging power and authority of the Columban church following the defeat in 664 of the Celtic Church in favour of Rome's style of administration and the timing of Easter, and concern for secular society and a desire for peace are some of the motives to be examined. In promulgating the law, Adomna?n must have anticipated certain outcomes that would ensure and preserve the Columban 'familia''s continuing supremacy. By tracing the history of Iona, the saint's cult, the law and ' Life of St. Columba', which was written by Adomna?n about the same time as he created his law, this thesis shows that, as a result of the challenges presented to the Iona community after 664, and as an act of piety for the society the 'familia' served, the ninth abbot, in garnering the support of prominent churchmen and secular leaders, ensured the continuing authority of the 'familia' for decades to come through this particular law.