The Anglo-Saxon Chronicle is the single most important primary source for the history of Anglo-Saxon England from its beginnings in the 5th century up to the Norman Conquest in 1066: without it very little would be known about the Viking Age in England. The Chronicle is not a single source but a group of related chronicles that all derive from a common original compiled during the reign of Alfred the Great of Wessex, probably in the late 880s or early 890s. Copies of this original chronicle were circulated to several centres, where they were subsequently kept up to date by local annalists. All versions of the Chronicle share virtually the same information up to 890-2, but there are considerable differences between them from 893 onwards. Most versions of the Chronicle were discontinued soon after the Norman Conquest, but at Peterborough it was continued until 1154. Seven manuscripts of the Chronicle, written in the original Old English have survived, and the existence of several others, now lost, is known from extracts quoted in later Latin sources and entries in medieval library catalogues.
Though it is written mostly in a detached, dispassionate style, the Chronicle is not an objective record of events and it was probably begun on Alfred's orders as part of a propaganda campaign to present the Wessex dynasty as the leading defender of the Christian English from the heathen Vikings.
Notes from Encyclopaedia of the Viking Age by John Haywood. Thames & Hudson 2000. pp23-4
This is one of a number of versions of the Anglo-Saxon Chronicle available online.