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Provenance

The poem is known only from a single manuscript, estimated to date from around 975–1025, in which it appears with other works. The manuscript therefore dates either to the reign of Æthelred the Unready, characterised by strife with the Danish king Sweyn Forkbeard, or to the beginning of the reign of Sweyn's son Cnut the Great from 1016. The Beowulf manuscript is known as the Nowell Codex, gaining its name from 16th-century scholar Laurence Nowell. The official designation is " British Library, Cotton Vitellius A.XV" because it was one of Sir Robert Bruce Cotton 's holdings in the Cotton library in the middle of the 17th century. Many private antiquarians and book collectors, such as Sir Robert Cotton, used their own library classification systems. "Cotton Vitellius A.XV" translates as: the 15th book from the left on shelf A (the top shelf) of the bookcase with the bust of Roman Emperor Vitellius standing on top of it, in Cotton's collection. Kevin Kiernan argues that Nowell most likely acquired it through William Cecil, 1st Baron Burghley, in 1563, when Nowell entered Cecil's household as a tutor to his ward, Edward de Vere, 17th Earl of Oxford.

The earliest extant reference to the first foliation of the Nowell Codex was made sometime between 1628 and 1650 by Franciscus Junius (the younger). The ownership of the codex before Nowell remains a mystery.

The Reverend Thomas Smith (1638–1710) and Humfrey Wanley (1672–1726) both catalogued the Cotton library (in which the Nowell Codex was held). Smith's catalogue appeared in 1696, and Wanley's in 1705. The Beowulf manuscript itself is identified by name for the first time in an exchange of letters in 1700 between George Hickes, Wanley's assistant, and Wanley. In the letter to Wanley, Hickes responds to an apparent charge against Smith, made by Wanley, that Smith had failed to mention the Beowulf script when cataloguing Cotton MS. Vitellius A. XV. Hickes replies to Wanley "I can find nothing yet of Beowulph." Kiernan theorised that Smith failed to mention the Beowulf manuscript because of his reliance on previous catalogues or because either he had no idea how to describe it or because it was temporarily out of the codex.

The manuscript passed to Crown ownership in 1702, on the death of its then owner, Sir John Cotton, who had inherited it from his grandfather, Robert Cotton. It suffered damage in a fire at Ashburnham House in 1731, in which around a quarter of the manuscripts bequeathed by Cotton were destroyed. Since then, parts of the manuscript have crumbled along with many of the letters. Rebinding efforts, though saving the manuscript from much degeneration, have nonetheless covered up other letters of the poem, causing further loss. Kiernan, in preparing his electronic edition of the manuscript, used fibre-optic backlighting and ultraviolet lighting to reveal letters in the manuscript lost from binding, erasure, or ink blotting.