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A term applied variously to: (i) a female holding the Crown in her own right, who has the same powers, prerogatives, and rights as a King has (Queen regnant); (ii) the spouse of a King (Queen consort); and (iii) the widow of a deceased King (Queen Dowager or Queen mother). The latter two categories of Queen hold no royal or political powers except for those that have been specially conferred, but are protected as to person by the Treason Act 1351. However, under British law a Queen regnant has all the same powers as a King.

The title to the Crown of the current Queen regnant, Elizabeth II, is based on the Act of Settlement 1700 and the Union with Scotland Act 1706, together with certain other statutes. She is an essential element of Parliament, head of the British armed forces, supreme governor on earth of the Church of England, and Head of the Commonwealth of Nations.