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The Group of Eight (G8) is a forum for the governments of the world's eight wealthiest countries. The forum originated with a 1975 summit hosted by France that brought together representatives of six governments: France, West Germany, Italy, Japan, the United Kingdom, and the United States, thus leading to the name Group of Six or G6. The summit became known as the Group of Seven or G7 the following year with the addition of Canada. The G7, that is active even after the creation of the G8, is composed by 7 of 8 of the wealthiest countries on Earth (as net wealth and not GDP). In 1997, Russia was added to the group which then became known as the G8. The European Union is represented within the G8 but cannot host or chair summits.
"G8" can refer to the member states in aggregate or to the annual summit meeting of the G8 heads of government. The former term, G6, is now frequently applied to the six most populous countries within the European Union. G8 ministers also meet throughout the year, such as the G7/8 finance ministers (who meet four times a year), G8 foreign ministers, or G8 environment ministers.
Collectively, the G8 nations comprise 50.1% of 2012 global nominal GDP and 40.9% of global GDP (PPP). Each calendar year, the responsibility of hosting the G8 rotates through the member states in the following order: France, United States, United Kingdom, Russia, Germany, Japan, Italy, and Canada. The holder of the presidency sets the agenda, hosts the summit for that year, and determines which ministerial meetings will take place. Lately, both France and the United Kingdom have expressed a desire to expand the group to include five developing countries, referred to as the Outreach Five (O5) or the Plus Five: Brazil, People's Republic of China, India, Mexico, and South Africa. These countries have participated as guests in previous meetings, which are sometimes called G8+5.
With the G-20 major economies growing in stature since the 2008 Washington summit, world leaders from the group announced at their Pittsburgh summit on September 25, 2009, that the group will replace the G8 as the main economic council of wealthy nations.

http://en.wikipedia.org/wiki/G8