Commonwealth Day is the annual celebration of the Commonwealth of Nations, often held on the second Monday in March. It is marked by a service in Westminster Abbey, normally attended by Queen Elizabeth II as Head of the Commonwealth, along with the Commonwealth Secretary-General and Commonwealth High Commissioners in London. The Queen delivers an address to the Commonwealth, which is broadcast throughout the world.
The Commonwealth of Nations, generally known simply as the Commonwealth, is a political association of 54 member states, almost all of which are former territories of the British Empire.
The Commonwealth dates back to the first half of the 20th century with the decolonisation of the British Empire through increased self-governance of its territories. It was originally created as the British Commonwealth of Nations through the Balfour Declaration at the 1926 Imperial Conference, and formalised by the United Kingdom through the Statute of Westminster in 1931. The current Commonwealth of Nations was formally constituted by the London Declaration in 1949, which modernised the community and established the member states as “free and equal”.
The Commonwealth and Britain have a shared history, cultural links, common legal systems and business practices. Following a 1973 proposal by the Royal Commonwealth Society, the Commonwealth Secretariat selected the second Monday in March as the date on which Commonwealth Day is observed throughout all countries of the Commonwealth.