The Great Seal of the Realm is a seal that is used to symbolise the sovereign's approval of state documents. It is also known as the Great Seal of the United Kingdom (known prior to the Treaty of Union of 1707 as the Great Seal of England; and from then until the Union of 1801 as the Great Seal of Great Britain). To make it, sealing wax is melted in a metal mould or matrix and impressed into a wax figure that is attached by cord or ribbon to documents that the monarch wishes to seal officially. The formal keeper of the seal is the Lord High Chancellor of Great Britain.

Scotland has had its own great seal since the 14th century. The Acts of Union 1707, joining the kingdoms of Scotland and England, provided for the use of a single Great Seal for the new Kingdom of Great Britain.^[1] However, it also provided for the continued use of a separate Scottish seal to be used there, and this seal continues to be called the Great Seal of Scotland, although it is not technically one. Similarly, a separate Great Seal of Ireland, which had been used in Ireland since the 13th century, continued in use after the union of 1801, until the secession of the Irish Free State, after which a new Great Seal of Northern Ireland was created for use in Northern Ireland. A new Welsh Seal was introduced in 2011.

At some time before the year 1066 Edward the Confessor began to use a "Great Seal", which created a casting in wax of his own face, to signify that a document carried the force of his will. With some exceptions, each subsequent monarch up to 1603, when the king of Scotland succeeded to the throne of England, chose his or her own design for the Great Seal.

Levina Teerlinc is believed to have designed the seal of Queen Mary I, and also the earliest seal used by her successor Elizabeth I, in the 1540s.^[2]

When opening Parliament on 3 September 1654, the Lord Protector Oliver Cromwell was escorted by the three "Commissioners of the Great Seal of the Commonwealth of England", who were Whitelock, Lisle, and Widdrington. This Seal was inscribed with "The Great Seal of England, 1648", displaying a map of England, Ireland, Jersey, and Guernsey on one side, with the Arms of England and Ireland. On the other side was shown the interior of the House of Commons, the Speaker in his chair, with the inscription, "In the first year of Freedom, by God's blessing restored, 1648." In 1655, Cromwell appointed three Commissioners of the Great Seal of Ireland, Richard Pepys, Chief Justice of the Upper Bench, Sir Gerard Lowther, Chief Justice of the Common Bench; and Miles Corbet, Chief Baron of the Exchequer. But they held the seal only until 1656, when Cromwell nominated William Steele, Chief Baron of the Court of Exchequer in England, Lord Chancellor of Ireland.^[3]

In 1688, while attempting to flee to France during the Glorious Revolution, James II allegedly attempted to destroy his Great Seal by throwing it into the River Thames, in the hope that the machinery of government would cease to function. James's successors, William III and Mary II, used the same seal matrix in their new Great Seal. This may have been a deliberate choice, in order to imply the continuity of government. A new obverse was created, but the reverse was crudely adapted by inserting a female figure beside the male figure. When Mary died, the obverse returned to the design used by James II, while the female figure was deleted from the reverse. Thus, William III used a seal that was identical to James II's, except for changes to the legend and coat of arms.^[4]

Edward VIII, who abdicated only a few months after succeeding to the throne, never selected a design for his own seal and continued to use that of his predecessor, George V. Only one matrix of the Great Seal exists at a time, and since the wax used for the Great Seal has a high melting point, the silver plates that cast the seal eventually wear out. The longer-lived British monarchs have had several Great Seals during their reigns, and Queen Victoria had to select four different Great Seal designs during her sixty-three years on the throne.^[5]

The last seal matrix of Elizabeth II was authorised by the Privy Council in July 2001.^[6] It was designed by James Butler and replaced that of 1953, designed by Gilbert Ledward. The obverse shows the middle-aged Elizabeth II enthroned and robed, holding in her right hand a sceptre and in her left the orb. The circumscription is an abbreviated form of the royal titles in Latin: elizabeth · ii · d·g· britt· regnorvmqve · svorvm · ceter· regina · consortionis · popvlorvm · princeps · f·d·, lit. 'Elizabeth the Second, by the Grace of God, of the Britains and of her other realms Queen, Head of the Commonwealth, Defender of the Faith'.^[7] On the reverse are the full royal arms, including crest, mantling and supporters. This is the first time that the royal arms have provided the main design for one side of the English or British Great Seal. The obverse of the 1953 version depicted the Queen on horseback, dressed in uniform and riding sidesaddle, as she used to attend the annual Trooping the Colour ceremony for many years until the late 1980s. The seal's diameter is 6 inches (150 mm), and the combined weight of both sides of the seal matrix exceeds 275 troy ounces (302 oz; 8,600 g). Charles III, as of 2024, uses the seal of his mother and predecessor, having directed by Order in Council on 10 September 2022, "that the Lord High Chancellor of Great Britain is authorised to make use of the Great Seal for sealing all things whatsoever that pass the Great Seal until another Great Seal be prepared and authorised by His Majesty".^[8][9]

The Great Seal is attached to the official documents of state that require the authorisation of the monarch to implement the advice of His Majesty's Government.

Under today's usage of the Great Seal, seals of dark green wax are affixed to letters patent elevating individuals to the peerage, blue seals authorise actions relating to the Royal family, and scarlet seals appoint bishops and implement various other affairs of state. In some cases the seal is replaced by a wafer version,^[10] a smaller representation of the obverse of the Great Seal embossed on coloured paper attached to the document being sealed. This simpler version is used for royal proclamations, letters patent granting royal assent to legislation, writs of summons to Parliament, licences for the election of bishops, commissions of the peace, and many other documents.^[11] It formerly constituted treason to forge the Great Seal.^[12]

The Great Seal of the Realm is in the custody of and is administered by the Lord Keeper of the Great Seal. This office has been held jointly with that of Lord Chancellor since 1761. The current Lord Chancellor is Alex Chalk. The Constitutional Reform Act 2005 reiterates that the Lord Chancellor continues to be the custodian of the Great Seal.^[13] Though, in the past, the Great Seal has been delivered to and remained in the custody of the Sovereign when it has been used to seal instruments that related to or granted gifts or emoluments to the Lord Chancellor.^[14]

The Clerk of the Crown in Chancery, who is also Permanent Secretary of the Ministry of Justice, heads His Majesty's Crown Office, and is responsible for the affixing of the Great Seal. They are assisted by the Deputy Clerk of the Crown. Day-to-day custody is entrusted to the Clerk of the Chamber, and subordinate staff include a Sealer and two Scribes to His Majesty's Crown Office.

Section 2 of the Great Seal Act 1884 governs the use of the Great Seal of the Realm:

2 - (1) A warrant under Her Majesty’s Royal Sign Manual, countersigned by the Lord Chancellor, or by one of Her Majesty’s Principal Secretaries of State, or by the Lord High Treasurer, or two of the Commissioners of Her Majesty’s Treasury, shall be a necessary and sufficient authority for passing any instrument under the Great Seal of the United Kingdom, according to the tenor of such warrant; Provided that any instrument which may now be passed under the Great Seal by the fiat or under the authority or directions of the Lord Chancellor or otherwise without passing through any other office may continue to be passed as heretofore.

(2) The Lord Chancellor may from time to time make, and when made revoke and vary, regulations respecting the passing of instruments under the Great Seal of the United Kingdom, and respecting the warrants for that purpose, and the preparation of such instruments and warrants, and every such warrant shall be prepared by the Clerk of the Crown in Chancery.

(3) No person shall make or prepare any warrant for passing any instrument under the Great Seal of the United Kingdom, or procure any instrument to be passed under that Seal otherwise than in manner provided by this Act or the Crown Office Act 1877; and any person who acts in contravention of this section shall be guilty of a misdemeanour.

The Great Seal for each successive monarch is inscribed with the monarch's style (in Latin) on both sides of the seal. Some of those used in the past are shown below.^[15][16] Where the inscriptions on both sides of the seal are identical, only one is given. Where they are the same except for the use of abbreviations, the one with the fuller forms is given. Where they are different, they are shown separated by a slash.

• Great Seal
• Great Seal of Scotland
• Great Seal of Northern Ireland
• Welsh Seal