The Synod of Whitby (664 A.D.) was a Northumbrian synod where King Oswiu of Northumbria ruled that his kingdom would calculate Easter and observe the monastic tonsure according to the customs of Rome, rather than the customs practised by Irish monks at Iona and its satellite institutions. The synod was summoned at Hilda's double monastery of Streonshalh (Streanæshalch), later called Whitby Abbey.
There are two principal sources for the synod. The first source, the Life of Wilfrid, is a hagiographic work written by Stephen of Ripon, often identified as Eddius Stephanus, probably soon after 710. The second source is the Historia Ecclesiastica gentis Anglorum by the Venerable Bede, written in 731. One of Bede's sources was the Life of Wilfrid itself, but he also had access to people who knew participants in the synod. For example, Bede knew Acca of Hexham, and dedicated many of his theological works to him. Acca was a companion of Wilfrid's on some of his journeys to Rome.
Both accounts basically agree, though Bede gives a much lengthier discourse on the debate. The description of the proceedings, where King Oswiu presides and rules but does not engage in the ecclesiastics' debate himself, parallels examples of other synods in other sources, such as one in the Vita Sancti Bonifati by Willibald (where King Ine of Wessex performed the same function as Oswiu). Nonetheless, it is important to observe that the authors, despite their relatively good access to sources concerning the synod, still wrote at a distance, and the accounts, especially the quotations attributed to the participants, are more likely to be summaries of how Bede and Stephen understood the issue rather than something like true quotations. Further, the motivations of the authors influenced how they presented the material. Bede placed his description of the event centrally in his narrative, and he has been recognised as overemphasising the historical significance of the synod because Easter calculation was of special interest to him, and also because he wished to stress the unity of the English Church. However, Bede's accuracy as a historian has been well regarded by Anglo-Saxon scholars, and historians have generally been comfortable following Bede's basic presentation of the synod. Stephen's text has found more criticism, and Reginald Poole identified many of his inaccuracies, but Stephen's account of the synod did not suffer the same criticism as other passages in his work.