Some G20 participants, as well as commentators, suggested that the G20 should replace the G7 as the most important forum for coordinating international economic policy. What is with all these Gs, and what do they do? Here is my quick list of important G- summits, and their members:
G7: This is a meeting of the finance ministers of Canada, France, Germany, Italy, Japan, the United Kingdom, and the United States.
G8: This is a meeting of the heads of state of the G7 countries, plus Russia. Fun fact: after shirtless pictures of Sarkozy and Putin emerged a couple years ago, snarky journalists suggested a "G8 calendar".
G20: This is a meeting of finance ministers and central bank heads from 20 countries, including the G8 countries, Australia, whichever country is the current president of the EU (provided that country is not already included), and 10 large emerging market economies: Argentina, Brazil, China, India, Indonesia, Mexico, Saudi Arabia, South Africa, South Korea, and Turkey.
G2: Not really an official designation, this is sometimes used to refer to China and the United States. The idea is that agreements between these two countries could become necessary and sufficient to drive international policies.
Besides generating fun photo ops, the G7, G8 and G20 meetings allow countries to meet to coordinate policy on security, economics, and the environment. The efficacy of these meetings is limited by the fact that the members are sovereign nations, so any agreements that might be reached are only worth as much as each nation's commitment to hem (and domestic political realities!) While the G8 may retain importance on security, in part because of the difficulty in coordinating policy among 20 countries, it is very likely that G20 will indeed become the more important forum for economic policy-- it seems bizarre to discuss the global economy without China, and developing economies are becoming a larger share of the world economy. The IMF projects that the G7 share of world GDP will drop below 50% in 2014, down from near 70% in the early 1990s.
Final fun fact: At summits such as the G7 or G20 summits, the person who in charge of the meeting for each country (who develops materials, schedules officials' participation, etc.) is called the "Sherpa". (They help you up the summit, haha, get it?) Borrowing from the culinary world, the Sherpa's deputy is known as the Sous-Sherpa.