A fyrd (Old English pronunciation: [fyrˠd]) was a type of early Anglo-Saxon army that was mobilised from freemen or paid men to defend their Shire's lords estate, or from selected representatives to join a royal expedition. Service in the fyrd was usually of short duration and participants were expected to provide their own arms and provisions. The composition of the fyrd evolved over the years, particularly as a reaction to raids and invasions by the Vikings. The system of defence and conscription was reorganised during the reign of Alfred the Great, who set up 33 fortified towns (or burhs) in his kingdom of Wessex. The amount of taxation required to maintain each town was laid down in a document known as the Burghal Hidage. Each lord had his individual holding of land assessed in hides. Based on his land holding, he had to contribute men and arms to maintain and defend the burhs. Non-compliance with this requirement could lead to severe penalties.

Ultimately the fyrd consisted of a nucleus of experienced soldiers that would be supplemented by ordinary villagers and farmers from the shires who would accompany their lords.