Elizabeth II becomes the longest reigning monarch of the United Kingdom.

Elizabeth II was Queen of the United Kingdom and other Commonwealth realms from 6 February 1952 until her death. She had been queen regnant of 32 sovereign states during her lifetime and was the monarch of 15 realms at her death. Her reign of 70 years and 214 days is the longest of any British monarch, the second-longest of any sovereign state, and the longest of any queen regnant in history.

The following is a list, ordered by length of reign, of the monarchs of the United Kingdom of Great Britain and Northern Ireland (1927–present), the United Kingdom of Great Britain and Ireland (1801–1922), the Kingdom of Great Britain (1707–1801), the Kingdom of England (871–1707), the Kingdom of Scotland (878–1707), the Kingdom of Ireland (1542–1800), and the Principality of Wales (1216–1542).