The Group of Eight (G8, and formerly the G6 or Group of Six and also the G7 or Group of Seven) is a forum, created by France in 1975, for governments of six countries in the world: France, Germany, Italy, Japan, the United Kingdom, and the United States. In 1976, Canada joined the group (thus creating the G7).
In becoming the G8, the group added Russia in 1997. In addition, the European Union is represented within the G8, but cannot host or chair.The EU has the privileges and obligations of membership but does not host/chair summits. It is represented by the Commission and Council Presidents.
"G8" can refer to the member states 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.
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, 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. 
- The Unaccountable G-8 Project Syndicate, June 30, 2010