In the Commonwealth realms, a Royal Style and Titles Act or a Royal Titles Act is an Act of Parliament passed in the relevant jurisdiction which defines the sovereign's formal title in that jurisdiction. The most significant of these acts is the Royal and Parliamentary Titles Act 1927 of the United Kingdom, which recognised the creation of the Irish Free State, a development that necessitated a change in King George V's title.
In December 1952, the governments of Commonwealth realms agreed that each realm would adopt its own royal titles.
In Australia, the monarch's title has been since 1973: "Elizabeth the Second, by the Grace of God Queen of Australia and Her other Realms and Territories, Head of the Commonwealth". Typically, though, the sovereign is styled Queen of Australia and is addressed as such when in Australia or performing duties on behalf of Australia abroad. The sovereign is the only member of the Royal Family to have a title established through Australian law; other members are accorded a title via letters patent in the United Kingdom.
The Canadian parliament passed in 1947 the Royal Style and Titles Act and an Order in Council was issued on 22 June the following year to remove the term Emperor of India from the sovereign's Canadian title. In 1953, the Canadian parliament passed the Royal Style and Titles Act, consenting to the issue of a royal proclamation changing the royal style and titles. Subsequently, the relevant royal proclamation was issued on May 28 declaring the official styles in Canada to be, in English: Elizabeth the Second, by the Grace of God of the United Kingdom, Canada and Her other Realms and Territories Queen, Head of the Commonwealth, Defender of the Faith, and, in French: Elizabeth Deux, par la grâce de Dieu Reine du Royaume-Uni, du Canada et de ses autres royaumes et territoires, Chef du Commonwealth, Défenseur de la Foi.
The Royal Titles Act 1901 allowed for the addition of the words "and of the British Dominions beyond the Seas" to the monarch's title.
The Royal and Parliamentary Titles Act 1927 was amended in 1948 by the Indian Independence Act 1947 so as to omit the words Emperor of India from the monarch's title in the United Kingdom. King George VI's title became: George VI by the Grace of God of Great Britain, Ireland and the British Dominions beyond the Seas King, Defender of the Faith.
The Royal Titles Act 1953 specified that it applied only to the United Kingdom and those overseas territories whose foreign relations were controlled by the UK. The legislation tidied up the use of the title King of Ireland, following Ireland's transition to a republic in 1949.
As authorised by the Act, Elizabeth proclaimed that her title in the United Kingdom would be, equivalently in English and (or the first time) in Latin: "Elizabeth II, 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" and Elizabeth II, Dei Gratia Britanniarum Regnorumque Suorum Ceterorum Regina, Consortionis Populorum Princeps, Fidei Defensor.