大宪章（拉丁语：Magna Carta，英语：The Great Charter）又称作自由大宪章（拉丁语：Magna Carta Libertatum，英语：The Great Charter of the Liberties），是英格兰国王约翰最初于1215年6月15日在温莎附近的兰尼米德订立的拉丁文政治性授权文档；但在随后的版本中，大部分对英国王室绝对权力的直接挑战条目被删除；1225年首次成为法律；1297年的英文版本至今仍然是英格兰威尔士的有效法律。

这份由坎特伯里大主教史蒂芬·朗顿起草的大宪章乃封建贵族用来对抗英国国王（主要是针对当时的约翰）权力的封建权利保障协议。订立大宪章的主因是教皇、英王约翰及封建贵族对王室权力出现意见分歧。大宪章要求王室放弃部分权力，保护教会的权力，尊重司法过程，接受王权受法律的限制。大宪章是英国在创建宪法政治这长远历史过程的开始。

Magna Carta (Latin for "the Great Charter"), also called Magna Carta Libertatum (Latin for "the Great Charter of the Liberties"), is a charter agreed by King John of England at Runnymede, near Windsor, on 15 June 1215. First drafted by the Archbishop of Canterbury to make peace between the unpopular King and a group of rebel barons, it promised the protection of church rights, protection for the barons from illegal imprisonment, access to swift justice, and limitations on feudal payments to the Crown, to be implemented through a council of 25 barons. Neither side stood behind their commitments, and the charter was annulled by Pope Innocent III, leading to the First Barons' War. After John's death, the regency government of his young son, Henry III, reissued the document in 1216, stripped of some of its more radical content, in an unsuccessful bid to build political support for their cause. At the end of the war in 1217, it formed part of the peace treaty agreed at Lambeth, where the document acquired the name Magna Carta, to distinguish it from the smaller Charter of the Forest which was issued at the same time. Short of funds, Henry reissued the charter again in 1225 in exchange for a grant of new taxes; his son, Edward I, repeated the exercise in 1297, this time confirming it as part of England's statute law.