Provisions of Oxford

The Provisions of Oxford were constitutional reforms developed in 1258 which resolved a dispute between the English barons and King Henry III of England. They asserted the right of the barons to representation in the king's government and, like the earlier Magna Carta (great charter), demonstrated the ability of the barons to press their concerns in opposition to the monarchy.
Setting.
When in the spring of 1258 Henry III sought financial aid from Parliament, he was confronted by a group of barons who insisted on a new commission of reform, in the shape of a council of twenty-four members, twelve selected by the crown, twelve by the barons. The Provisions of Oxford were the reform programme the twenty-four members, including Simon de Montfort, 6th Earl of Leicester, set out for.
Provisions.
The Provisions set up a new form of government, with a 15-member Privy Council (nine baronial) to advise the king and oversee the entire administration as a standing body. They also confirmed that "there be three parliaments a year...to treat of the common wants of the kingdom, and of the king." At the parliaments, the Fifteen would be checked and monitored by another body of twelve representative barons. Meanwhile the men selected (by four electors appointed by the Twenty-four) were to supervise ministerial appointments, local administration and the custody of royal castles; while recommendations for an inquest into local (mis-)government, and further measures of reform were also set out.
Linguistic innovation.
A written confirmation of the agreement was sent to the sheriffs of all the counties of England trilingually, in Latin, French and, significantly, in Middle English. The use of the English language was symbolic of the "Anglicisation" of the government of England and an antidote to the Francization which had taken place in the decades immediately before. The Provisions were the first government documents to be published in English since the Norman Conquest two hundred years before.
Later developments.
The Provisions of Oxford were confirmed and extended in 1259 by the Provisions of Westminster. The administrative controls of the Provisions of Oxford were overthrown by Henry, helped by a papal bull, in 1261, seeding the start of the Second Barons' War (1263–1267), which was won by the King and his royalist supporters; and they were annulled for the last time in 1266 by the Dictum of Kenilworth. However the administrative and legislative reforms the barons had initiated were taken up and confirmed in the Statute of Marlborough. 
The 1258 Provisions had a significant effect upon the development of the English Common Law, limiting in part the expansion of royal jurisdiction by way of the number of available writs, but in the main confirming the importance of the common law of the land for all, from king to commoner. 