This is an important symbolic and unifying role. As Head, The Queen personally reinforces the links by which the Commonwealth joins people together from around the world.
One of the ways of strengthening these connections is through regular Commonwealth visits.
During her reign, The Queen has visited every country in the Commonwealth (with the exception of Cameroon, which joined in 1995 and Rwanda which joined in 2009) and made many repeat visits. One third of The Queen's total overseas visits are to Commonwealth countries.
The Duke of Edinburgh, The Prince of Wales and other members of the Royal Family are also regular visitors to the Commonwealth.
The Queen keeps in touch with Commonwealth developments through regular contact with the Commonwealth Secretary General and his Secretariat. This is the Commonwealth's central organisation.
Based in London, it co-ordinates many Commonwealth activities. Her Majesty also has regular meetings with Heads of Government from Commonwealth countries.
Each year, The Queen attends the Commonwealth Day celebrations in London. Since 1977, Commonwealth Day has been celebrated throughout the Commonwealth on the second Monday in March.
The Queen attends an inter-denominational service held in Westminster Abbey, followed by a reception hosted by the Commonwealth Secretary General.
Modern communications technology allows The Queen to speak to every part of the Commonwealth through her annual Christmas and Commonwealth Day messages.
Both messages are delivered by The Queen as Head of the Commonwealth to the peoples of the Commonwealth as a whole. They are unique in that they are delivered on The Queen's own responsibility, drafted without ministerial advice.
Every two years a meeting of the Commonwealth Heads of Government (CHOGM) is held, at locations throughout the Commonwealth.
The Queen is normally present in the host country, during which she has a series of private meetings with the Commonwealth countries' leaders.
The Commonwealth Games are a major sporting occasion which brings together young people from all over the world in friendly competition.
The Queen often attends the Commonwealth Games to open or close them - most recently, the 2006 Commonwealth Games in Melbourne, Australia.
In all these different ways The Queen, though not part of the machinery of government in the Commonwealth, acts as a personal link and human symbol of the Commonwealth as an international organisation.
Instead of the Royal standard, The Queen uses special flags when she visits the Commonwealth.
She has a personal flag - an initial E and crown within a chaplet of roses - for use at Commonwealth meetings.
In realms such as Canada, Australia and New Zealand, The Queen uses a different standard for each individual country.
