The Assize of Northampton, largely based on the Assize of Clarendon of 1166, is among a series of measures taken by King Henry II of England that solidified the rights of the knightly tenants and made all possession of land subject to and guaranteed by royal law.
The assize is believed to have been passed at a council held in Northampton in January 1176. The assize contained severe penalties for various offences and gave the justices substantial powers at the expense of the sheriffs. The assize is connected with the reorganisation of itinerant justices and contains instructions for six groups of justices appointed to tour the country. Later clauses deal with the introduction of important new legislation, chiefly the king's right to have certain cases brought into his court.
The assize was a strong response to a crime-wave then being experienced and gave additional powers to the authorities by creating new offences that a judge could examine, including arson and forgery, and set down new and severe punishments that could be handed down, including the removal of an offender's right hand.
The Assize of Northampton is also the first official document to contain information on the possessory assizes of mort d'ancestor and novel disseisin.