"On September 25, 1999 in Washington, D.C., the Finance Ministers of the Group of Seven (G-7) leading industrialized nations announced the creation of the Group of Twenty (G-20). This international forum of Finance Ministers and Central Bank Governors represents 19 countries, the European Union and the Bretton Woods Institutions (the International Monetary Fund/IMF -- and the World Bank).
"The creation of the G-20 fulfilled the commitment by G-7 leaders at the June 1999 Summit at Köln "…to establish an informal mechanism for dialogue among systemically important countries within the framework of the Bretton Woods institutional system."
"Like the G-7, but unlike larger international organizations such as the United Nations, the World Bank and the IMF, the G-20 has no permanent Secretariat. The size and structure of the G-20 is designed to encourage the informal exchange of views and the formation of consensus on international economic and financial issues. Each year, a temporary Secretariat is established by the chairing country with the objective of coordinating the work of the Group and organizing the meetings."
"The G-20 promotes discussion, and studies and reviews policy issues among industrialized countries and emerging markets with a view to promoting international financial stability."
"The Managing Director of the IMF and the President of the World Bank, as well as the Chairpersons of the International Monetary and Financial Committee and Development Committee of the IMF and World Bank, participate fully in the discussions."
"Finance Minister Paul Martin of Canada was selected to be the inaugural chairperson of the G-20. The first three meetings were chaired by Minister Martin in Berlin, December 1999, in Montreal, October 2000 and in Ottawa, November 2001. In March 2002 the Chairmanship of the Group was taken over by India, in the figure of Mr. Jaswant Singh, Finance Minister. As of January 2003, the Chairmanship of the group was handed to Mexico. Mr. José Francisco Gil Díaz, Mexican Minister of Finance and Public Credit, will act as Chairperson of the G-20 throughout this year."
Source: G20 web site.
A G20 meeting was held in Melbourne (Australia) on 18–19 November 2006. 
The G20 includes the G8 (Britain, Canada, France, Germany, Italy, Japan, Russia and the United States) plus Argentina, Australia, Brazil, China, India, Indonesia, Mexico, Saudi Arabia, South Africa, South Korea and Turkey. The European Union, which also "sits at the table," is represented by the country that holds the EU rotating presidency, which is currently Italy.
27 October 2003: "G20 sees global recovery under way", AFP: "The G20 welcomed signs of a brightening outlook, but participants also sounded alarm over global economic imbalances, reflecting deepening concern over the US trade deficit."