The Commonwealth of Nations, usually known as the Commonwealth and sometimes as the British Commonwealth, is a voluntary association of 53 independent sovereign states, most of which are former British colonies (the exceptions being the United Kingdom itself and Mozambique).

The Commonwealth is an international organisation through which countries with diverse social, political, and economic backgrounds co-operate within a framework of common values and goals, outlined in the Singapore Declaration. These include the promotion of democracy, human rights, good governance, the rule of law, individual liberty, egalitarianism, free trade, multilateralism, and world peace.

Queen Elizabeth II is the Head of the Commonwealth, recognised by each state, and as such is the symbol of the free association of the organisation's members. This position, however, does not imply political power over Commonwealth member states. In practice, the Queen heads the Commonwealth in a symbolic capacity, and it is the Commonwealth Secretary-General who is the chief executive of the organisation. The Commonwealth is not a political union, and does not allow the United Kingdom to exercise any power over the affairs of the organisation's other members. Elizabeth II is also the Head of State, separately, of sixteen members of the Commonwealth, called Commonwealth realms. As each realm is an independent kingdom, Elizabeth II, as monarch, holds a distinct title for each, though, by a Prime Ministers' Conference in 1952, all include the words "Head of the Commonwealth" at the end; for example: Elizabeth the Second, by the Grace of God, Queen of Australia and of Her other Realms and Territories, Head of the Commonwealth. Beyond the realms, the majority of the members of the Commonwealth have their own, separate Heads of State: thirty-two members are Commonwealth republics and five members have their own monarchs (Sultan of Brunei, King of Lesotho, Supreme Ruler of Malaysia, King of Swaziland, and King of Tonga).

Every four years the Commonwealth's members celebrate the Commonwealth Games, the world's second-largest multi-sport event after the Olympic Games.