Elizabeth II (Elizabeth Alexandra Mary; born 21 April 1926) is the Queen of 16 of the 53 member states in the Commonwealth of Nations. She is Head of the Commonwealth and Supreme Governor of the Church of England.

Upon her accession on 6 February 1952, Elizabeth became Head of the Commonwealth and queen regnant of seven independent Commonwealth countries: the United Kingdom, Canada, Australia, New Zealand, South Africa, Pakistan, and Ceylon. Her coronation service the following year was the first to be televised. From 1956 to 1992, the number of her realms varied as territories gained independence and some realms became republics. Today, in addition to the first four of the aforementioned countries, Elizabeth is Queen of Jamaica, Barbados, the Bahamas, Grenada, Papua New Guinea, Solomon Islands, Tuvalu, Saint Lucia, Saint Vincent and the Grenadines, Belize, Antigua and Barbuda, and Saint Kitts and Nevis. She is the world's oldest reigning monarch as well as Britain's longest-lived. If still reigning on 10 September 2015, she will have become the longest-reigning British head of state and the longest-reigning female monarch in history, surpassing Queen Victoria.

Elizabeth was born in London as the elder daughter of the Duke and Duchess of York, later King George VI and Queen Elizabeth, and educated privately at home. Her father acceded to the throne on the abdication of his brother Edward VIII in 1936, from which time she was the heir presumptive. She began to undertake public duties during the Second World War, in which she served in the Auxiliary Territorial Service. In 1947, she married Philip, Duke of Edinburgh, with whom she has four children: Charles, Anne, Andrew, and Edward.

Elizabeth's many historic visits and meetings include a state visit to the Republic of Ireland, the first state visit of an Irish president to the United Kingdom, and reciprocal visits to and from the Pope. She has seen major constitutional changes, such as devolution in the United Kingdom, Canadian patriation, and the decolonisation of Africa. She has also reigned through various wars and conflicts involving many of her realms.

In her capacity as queen of the United Kingdom, Elizabeth II is styled, "Elizabeth the Second, by the Grace of God, of the United Kingdom of Great Britain and Northern Ireland and of Her other Realms and Territories Queen, Head of the Commonwealth, Defender of the Faith". The title "Defender of the Faith" reflects the Sovereign's position as the Supreme Governor of the Church of England, who is thus formally superior to the Archbishop of Canterbury. The original Latin phrase - Fidei Defensor - is referred to on all current British (and some Commonwealth) coins by the abbreviations F D or FID DEF. This reference was first added to British coins in 1714, during the reign of King George I. The decision of the Royal Mint to omit reference to the phrase (and other parts of the monarch's style) from the pre-decimal British "Godless Florin" in 1849, caused such a scandal that the coin was replaced.