Originally established as a vehicle for leading industrialised democracies to discuss the global economy, it has expanded its scope to issues such as peace, the environment and terrorism.
Often the atmosphere between the partners becomes tense in the run-up to the annual summit, held in the country which holds the rotating presidency.
However G7 summits traditionally end with a face-saving joint declaration regarding the most important outcomes of the meeting.
This year's summit promises to be fractious due to new import tariffs imposed by US President Donald Trump on his partners.
He has also called for the reintegration of Russia, a member of the group between 1998 and 2014 and which was thrown out after it annexed Ukraine's Crimea peninsula.
Origins in global economy
The meetings date back to Rambouillet in France in 1975, in the wake of the first oil shock, during which oil prices soared.
Six countries -- Britain, France, Germany, Italy, Japan and the United States -- took part in this first "G6", and were joined a year later by Canada making the "G7".
The initiative came from French president Valery Giscard d'Estaing who wanted to elevate to the top level meetings already held by the countries' finance ministers to tackle burning economic issues.
From G7 to G8
During the 1980s, tensions between the East and West during the Cold War gave a more political slant to the meetings.
The Williamsburg summit in 1983 adopted, for the first time, a declaration on security in Europe.
The text of support for the policies of US president Ronald Reagan towards Moscow was adopted despite the reservations of French president Francois Mitterrand.
The collapse of the Soviet Union in late 1991 proved a gamechanger.
Russia, which attended the summit as a guest in 1992, was in 1998 allowed for the first time to attend all summit meetings. The grouping was officially renamed the "G8".
Exclusive club criticised
From 1999, during a period of successive financial crises, the G8 was criticised for being an exclusive club.
The rich powers therefore also started meeting with emerging countries in the new "G20" grouping, in an attempt to resolve or avoid these crises.
In 2001 the G8's summit in Genoa, Italy, was overshadowed by violent demonstrations by anti-globalisation protesters which left one person dead.
The protesters challenged the usefulness and legitimacy of the G8 and called for the cancellation of the poorest countries' debts.
Protests dogged other G8 summits, which from then on were held under tight security.
Putin and Trump
In 2014 Vladimir Putin's Russia was suspended from the G8 after it annexed Ukraine's Crimea peninsula and sanctions were imposed on Moscow. The G8 summit planned for that year in Russia was cancelled and the G8 reverted to being the G7.
In 2017 the G7's unity was shattered on the issue of climate change during its first summit with Trump in Sicily. Several days later he decided to pull out of the Paris climate accord.
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