Adomnán or Adamnán of Iona (Old Irish pronunciation: [ˈaðəṽˌnaːn], Latin: Adamnanus, Adomnanus; c. 624 – 704), also known as Eunan (/ˈjuːnən/ YOO-nən; from Irish Naomh Ádhamhnán), was an abbot of Iona Abbey (r. 679–704), hagiographer, statesman, canon jurist, and saint. He was the author of the book on Saint Columba, the Vita was probably written between 697 and 700. The biography is by far the most important surviving work written in early medieval Scotland, and is a vital source for our knowledge of the Picts, and an insight into the life of Iona and the early medieval Gaelic monk.

Adomnán promulgated the Law of Adomnán or "Law of Innocents" (Latin: Lex Innocentium). He also wrote the treatise De Locis Sanctis (i.e. "On Holy Places"), an account of the great Christian holy places and centres of pilgrimage. Adomnán got much of his information from a Frankish bishop called Arculf, who had personally visited Egypt, Rome, Constantinople and the Holy Land, and visited Iona afterwards.

Adomnán was born about 624, a relative on his father's side of Columba. He was a member of the Northern Uí Néill lineage Cenél Conaill. He was the son of Rónán mac Tinne by Ronat, a woman from another Northern Uí Néill lineage known as the Cenél nÉnda. Adomnán's birthplace was probably in or near Raphoe, a town in what later became Tír Chonaill (now mainly County Donegal), in Ulster in the north of Ireland. Some of Adomnán's childhood anecdotes seem to confirm at least an upbringing in this fertile eastern part of present-day County Donegal, not far from the modern city of Derry.

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 Fáilbe mac Pípáin, 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,[4] and while this is not accepted by all scholars, it remains a strong possibility.

Iona Abbey
In 679, Adomnán became the ninth abbot of Iona after Columba.[5] 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 the Kingdom of 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.

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, 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. Jeffrey Wetherill sees Adomnán's long absences from Iona as having led to something of an undermining of his authority; he was thus unable to persuade the monks to adopt the Roman dating of Easter, let alone the tonsure.[2] It is clear that Adomnán did adopt that Roman dating, and moreover, probably did argue the case for it in Ireland.