With no headquarters, budget or permanent staff, the Group of Eight is an informal but exclusive body whose members set out to tackle global challenges through discussion and action.
The G8 comprises seven of the world's leading industrialised nations, and Russia.
The leaders of these countries meet face-to-face at an annual summit that has become a focus of media attention and protest action.
The G8's roots lie in the oil crisis and global economic recession of the early 1970s.
In 1973, these challenges prompted the US to form the Library Group - an informal gathering of senior financial officials from Europe, Japan and the US.
At the instigation of the French, the 1975 meeting drew in heads of government. The delegates agreed to meet annually. The six nations involved became known as the G6, and later the G7 and G8 after the respective entries of Canada (1976) and Russia (1998).
Though the G8 was set up as a forum for economic and trade matters, politics crept onto the agenda in the late 1970s. Recent summits have considered the developing world, global security, Middle East peace and reconstruction in Iraq.
G8 members can agree on policies and can set objectives, but compliance with these is voluntary. The G8 has clout in other world bodies because of the economic and political muscle of its members.
The workings of the G8 are a far cry from the "fireside chats" of the Library Group in the 1970s. Holed up behind fortress-like security, the delegates are accompanied by an army of officials. Elaborate preparations are made for their meetings, statements and photo-calls.
Nevertheless, G8 leaders strive to keep at least some of their encounters free from bureaucracy and ceremony. On the second day of their summit the leaders gather for an informal retreat, where they can talk without being encumbered by officials or the media.
The European Union is represented at the G8 by the president of the European Commission and by the leader of the country that holds the EU presidency. The EU does not take part in G8 political discussions.
The presidency of the G8 rotates between the group's member nations on an annual basis.
The country holding the presidency in a given year is responsible for hosting the annual summit and for handling the security arrangements.
As the foremost economic and political power in the G8, the US is regarded as the dominant member of the group, although this position is not formally enshrined.
Critics of the G8 have accused the body of representing the interests of an elite group of industrialised nations, to the detriment of the needs of the wider world.
Important countries with fast-growing economies and large populations, including China and India, are not represented. There are no African or Latin American members.
The G8's positive stance on globalisation has provoked a vigorous response from opponents, and riots have sometimes overshadowed summit agendas, most notably in Italy in 2001.
Since 2001, there has been a tendency for the summits to be held in more remote locations, with the aim of avoiding mass protests. The lengths to which security forces have gone to shield the politicians from demonstrators has served to reinforce the G8's closed-door image.
Within the last decade or so, the G8 has launched drives to counter disease, including HIV/Aids, and has announced development programmes and debt-relief schemes. Aid is often conditional on the respect for democracy and good governance in the recipient countries. Critics say that spending on such initiatives is inadequate.
Basic disagreements sometimes emerge within the G8: Global warming was a sticking point at the 2001 Genoa summit, where US President George W Bush underlined his rejection of the Kyoto treaty on emissions.
The subject was revisited at the 2007 Heiligendamm summit, where an agreement among leaders on the need to tackle climate change was hailed as an important step forward.
Since 2009, summit talks have focused on finding a common approach to stabilising the world economy and stimulating growth in the face of continuing global financial upheaval.