The origins of G8 date back to 1975, when the then French president Valéry Giscard d'Estaing invited the leaders of some of the world's richest industrialised nations to Rambouillet, near Paris, to discuss the economic problems of the day.
Present were the heads of state or government of France, the UK, the US, Germany, Italy and Japan.
The following year, Canada joined to create the G7 or "group of seven" and the group's membership remained the same until 1998, when Russia was invited to join and the name G8 was adopted.
The group holds annual summits to discuss current issues of international concern, also attended by the president of the European Commission and the head of government of the country holding the presidency of the European Union - currently Britain.
Unlike many other international bodies, the G8 does not have a fixed structure or a permanent administration.
Its informal nature allows the leaders of the largest economic and political powers to get together to discuss issues of common concern and set a global agenda for action.
Previous summits have resulted in agreements to create a global fund to fight Aids, tuberculosis and malaria; to establish an action plan for African development; to decommission nuclear facilities in Russia; to tackle money-laundering and to write off some of the debts owed by the world's poorest countries.
The G8 presidency rotates among the eight members and it is up to the country that holds it to set the agenda and to organise the annual summit. For many years, the G7 and G8 summits were held in the capitals or major cities of the host nation.
British prime minister Tony Blair hosted Britain's last summit in Birmingham in 1998 and London was the venue in 1978 and 1985.
However, violent anti-globalisation protests at the 2001 summit in Genoa, Italy, led to a trend for hosts to choose more remote venues.
Recent years have seen the summit take place behind tight security at the Rocky Mountain resort of Kananaskis, Canada (2002), the lakeside spa town of Evian in France (2003) and Sea Island, Georgia, in the US (2004).
Russia will host the G8 summit in St Petersburg in 2006, when it will hold the presidency for the first time. - (PA)