Saint Adomnán of Iona (627/8 – 704) was abbot of Iona (679-704), hagiographer, statesman and clerical lawyer; he was the author of the most important Vita of Saint Columba and promulgator of the "Law of Innocents", lex innocentium, also called Cáin Adomnáin, "Law of Adomnán". In Ireland, a popular anglicised form of his name is Saint Eunan from the Gaelic Naomh Adhamhnán.
It is thought that Adomnán may have begun his monastic career at a Columban monastery called Druim Tuamma, but any Columban foundation in northern Ireland or Dál Riata is a possibility, although Durrow is a stronger possibility than most. He probably joined the Columban familia (i.e. the federation of monasteries under the leadership of Iona Abbey) around the year 640. Some modern commentators believe that he could not have come to Iona until sometime after the year 669, the year of the accession of Abbot Failbe, the first abbot of whom Adomnán gives any information. However, Richard Sharpe argues that he probably came to Iona during the abbacy of Ségéne (d. 652). Whenever or wherever Adomnán received his education, Adomnán attained a level of learning rare in Early Medieval northern Europe. It has been suggested by Alfred Smyth that Adomnán spent some years teaching and studying at Durrow, and while this is not accepted by all scholars, remains a strong possibility.
In 679, Adomnán became the ninth abbot of Iona after Columba. Abbot Adomnán enjoyed a friendship with King Aldfrith of Northumbria. In 684, Aldfrith had been staying with Adomnán in Iona. In 686, after the death of Aldfrith's brother King Ecgfrith of Northumbria and Aldfrith's succession to the kingship, Adomnán was in Northumbria on the request of King Fínsnechta Fledach of Brega, in order to gain the freedom of sixty Gaels who had been captured in a Northumbrian raid two years before. This Adomnán achieved. Adomnán, in keeping with Ionan tradition, made several more trips to the lands of the English during his abbacy, including one the following year. It is sometimes thought, after the account given by Bede, that it was during his visits to Northumbria, under the influence of Abbot Ceolfrith of Jarrow, that Adomnán decided to adopt the Roman dating of Easter that had been agreed some years before at the Synod of Whitby. Bede implies that this led to a schism at Iona, whereby Adomnán became alienated from the Iona brethren, and went to Ireland to convince the Irish of the Roman dating. Bede's account is however rarely believed by historians working in the area, although it is clear that Adomnán did adopt that Roman dating, and moreover, probably did argue the case for it in Ireland.
In 697, it is generally believed that Adomnán promulgated the Cáin Adomnáin, meaning literally the "Canons" or "Law of Adomnán". The Cáin Adomnáin was promulgated amongst a gathering of Irish, Dal Ríatan and Pictish notables at the Synod of Birr. It is a set of laws designed, among other things, to guarantee the safety and immunity of various types of non-combatant in warfare. For this reason it is also known as the "Law of Innocents". It is the earliest initiative of this kind recorded from Europe, and as such is often regarded, however dubiously, as a proto-type for the Geneva Convention and the Universal Declaration of Human Rights.
Adomnán died in 704, and became a saint in Scottish and Irish tradition, as well as one of the most important figures in either Scottish or Irish history. His death and feast day are commemorated on September 23. Along with St. Columba, he is joint patron of the Diocese of Raphoe, which encompasses the bulk of County Donegal in the north west of Ireland.