The Barons' Letter of 1301 was written by seven English earls and 96 English barons to Pope Boniface VIII as a repudiation of his claim of feudal overlordship of Scotland and as a defence of the rights of King King Edward I of England as overlord of Scotland. It was, however, never sent. The letter survives in two copies, known as A and B, both held in the National Archives at Kew under the reference E 26. Historically they were held amongst the documents in the Exchequer, Treasury of the Receipt department.
The seals of the signatories to the letter survive in excellent condition. Although they are now detached from the document, they form the earliest contemporary group of true coats of arms, the rules of heraldry having only been established at around the start of the 13th century, and were stated for that reason by Lord Howard de Walden to be of very great value to students of heraldry. Many of the armorials also appear in the near contemporary Falkirk Roll of Arms made before the Battle of Falkirk in 1298 and in the near contemporaneous stained glass shields in Dorchester Abbey, Oxfordshire.
The letter was written by English barons (mainly feudal barons and a few barons by writ) as a repudiation to the pope of his claim to feudal overlordship of Scotland, which he had expressed in a papal bull dated 27 June 1299 at Agnani. The bull was addressed to King King Edward I of England and it was delivered by Robert Winchelsey, Archbishop of Canterbury at Sweetheart Abbey in Galloway, Scotland, on 26th or 27 August 1300. The bull is preserved in the National Archives at Kew under reference SC 7/6/10.