Commonwealth Day is the annual celebration of the Commonwealth of Nations on the second Monday in March every year, which is marked by a multi-faith service in Westminster Abbey attended by Her Majesty Queen Elizabeth II, Head of the Commonwealth, the Commonwealth Secretary-General and the Commonwealth High Commissioners in London. The Queen delivers an address to the Commonwealth which is broadcast throughout the world on the BBC.

After the death of Queen Victoria in 1901, her birthday May 24 was made an annual commemoration known as Empire Day. In 1958 Empire Day was renamed Commonwealth Day, and from 1977 it has been celebrated on the second Monday in March. The Monday on or before May 24 is still celebrated in Canada as Victoria Day.