The G8, or Group of Eight, is known mainly for its annual summits, which in recent years have attracted sizeable protests.
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The group started as a discussion forum for the leaders of the United States, Japan, West Germany, France, Great Britain and Italy in 1975, when then French president Valery Giscard d'Estaing invited his counterparts to a summit in Rambouillet.
Canada was invited to join the following year, and for the next two decades the group was known as the G7. The group's eighth member, Russia, joined in 1997.
Emerging economies have since overtaken many of the G8 economies in terms of economic output, but the make-up of the group has remained the same.
As the G8 does not have a permanent secretariat, its meetings are arranged by a rotating presidency, which each of its members holds for a year at a time. The current UK presidency will be followed by Russia next year.
Since rioting broke out at the Seattle WTO conference of 1999, G8 summits have attracted considerable protests from activists critical of globalisation and wealth inequality.
At the 2001 summit in Genoa, hundreds of protesters were injured in clashes with Italian police.
An Italian activist died after being shot by a police officer. Several protesters were charged for looting and property damage.
Thousands of demonstrators convened on the Gleneagles summit venue in Scotland during the UK's previous chairmanship of the G8 in 2005.
About 1,000 tried to breach the police cordon around the summit venue, and police reinforcements were flown in by helicopter.
The 2012 G8 summit was moved from Chicago to the more remote location of Camp David partly in anticipation of mass protests, which were called by the Occupy movement.
While demonstrations have tended to capture the headlines on recent G8 summits, the talks behind closed doors have produced relatively few concrete results. Commitments by the leaders relate mostly to global development.
For example, at their 2009 summit in L'Aquila, Italy, G8 leaders committed to providing $22bn over the following three years for improving food security worldwide.
An accountability report published by the G8 presidency last week said about $16bn of the sum had been disbursed as of April 2013, with Japan and the US having delivered on a little over one third of their commitments.
At the Gleneagles summit in 2005, G8 members made country-specific pledges to increase development aid. The report finds mixed results, noting that the financial crisis has led many to cut their aid budgets.
In contentious foreign policy issues, G8 leaders have had to find compromise formulations acceptable to the European member states, the United States and Russia.
On Syria, last year's declaration urged all parties to cooperate with UN supervisors and to fulfil commitments to Kofi Annan's peace plan. It refrained from criticism of either party in the conflict, instead "strongly condemning" recent terrorist strikes in the country.
The 2012 summit declaration touches on 39 other points, from climate change to economic growth and the transition in Libya.
The most concrete commitment in the document relates to founding the New Alliance for Food Security and Nutrition with the aim of accelerating the flow of private capital to agriculture in Africa.
The stated aim of the alliance is to lift 50 million people from poverty by 2022.
The G8's makeup largely reflects the state of the world in the time of the group's founding in the 1970s.
During the G8's 36-year existence, its members have been taken over in terms of economic output by emerging economies.
According to World Bank 2011 statistics, China is the world's second-largest economy, Brazil is number six and India number nine.
The Group of 20 was founded in 1999 partly in response to this change in world order. Despite this relative decline, G8 members still represent about 50% of the world's GDP.
In 2010, Britain's Prime Minister David Cameron was reported to be considering attaching the G8 summit to another event such as the annual UN General Assembly in New York during Britain's G8 presidency in 2013.
He said he would like the forum to concentrate on foreign and security policy, leaving economic matters to the G20.