The Battle of Basing, occurring around 22 January 871 at Basing in Hampshire, resulted in a Danish Viking army defeating the West Saxons, led by King Æthelred and his brother Alfred the Great. This confrontation followed a series of battles triggered by the Viking invasion of Wessex in late December 870, beginning with their occupation of Reading. The sequence included a West Saxon victory at Englefield, a Viking victory at Reading, and another West Saxon victory at Ashdown on about 8 January. The defeat at Basing prefaced a two-month pause before the next engagement at Meretun, where the Vikings were victorious again. Following these events, King Æthelred died shortly after Easter, on 15 April 871, leading to Alfred's ascension to the throne.

The chronological placement of the Battle of Basing is supported by the death of Bishop Heahmund at Meretun on 22 March 871, with the Anglo-Saxon Chronicle documenting Basing as two months prior, thus on 22 January. This dating is part of a series of battles and movements, starting with the Viking arrival in Reading on 28 December 870, although the exactness of these dates is considered approximate due to potential inaccuracies in the historical record.