The Group of 20 (G20) is an intergovernmental forum comprising 19 sovereign countries, the European Union (EU), and the African Union (AU). It works to address major issues related to the global economy, such as international financial stability, climate change mitigation and sustainable development, through annual meetings of heads of state and heads of government.

The 19 member states of the G20 account for around 85% of gross world product (GWP), 75% of international trade, 56% of the global population, and 60% of the world's land area; including the EU and AU, the G20 comprises 78.9% of global population and 83.9% of global CO_(2) emissions from fossil energy.

The G20 was founded in 1999 in response to several world economic crises. Since 2008, it has convened at least once a year, with summits involving each member's head of government or state, finance minister, or foreign minister, and other high-ranking officials; the EU is represented by the European Commission and the European Central Bank. Other countries, international organizations, and nongovernmental organizations are invited to attend the summits, some permanently.

The African Union joined as the 21st member at the 2023 summit in India and was officially represented at the 2024 summit in Brazil.

The G20 is the latest in a series of post–World War II initiatives aimed at international coordination of economic policy, which include institutions such as the "Bretton Woods twins", the International Monetary Fund and the World Bank, and what is now the World Trade Organization.

The G20 was foreshadowed at the Cologne summit of the G7 in June 1999, and formally established at the G7 Finance Ministers' meeting on 26 September 1999 with an inaugural meeting on 15–16 December 1999 in Berlin. Canadian finance minister Paul Martin was chosen as the first chairman and German finance minister Hans Eichel hosted the meeting.

A 2004 report by Colin I. Bradford and Johannes F. Linn of the Brookings Institution asserted the group was founded primarily at the initiative of Eichel, the concurrent chair of the G7. However, Bradford later described then-Finance Minister of Canada (and future Prime Minister of Canada) Paul Martin as "the crucial architect of the formation of the G20 at finance minister level", and as the one who later "proposed that the G20 countries move to leaders level summits".

Canadian academic and journalistic sources have also identified the G20 as a project initiated by Martin and his American counterpart then-Treasury Secretary Larry Summers. All acknowledge, however, that Germany and the United States played a key role in bringing their vision into reality.

The G20's primary focus has been governance of the global economy. Summit themes have varied from year to year. The theme of the 2006 G20 ministerial meeting was "Building and Sustaining Prosperity". The issues discussed included domestic reforms to achieve "sustained growth", global energy and resource commodity markets, reform of the World Bank and IMF, and the impact of demographic changes.

In 2007, South Africa hosted the secretariat with Trevor A. Manuel, South African Minister of Finance as chairperson of the G20.

In 2008, Guido Mantega, Brazil's Minister of Finance, was the G20 chairman and proposed dialogue on competition in financial markets, clean energy, economic development and fiscal elements of growth and development.

The Summit of G20 Finance Ministers and Central Bank Governors, who prepare the leaders' summit and implement their decisions, was created as a response both to the 2008 financial crisis and to a growing recognition that key emerging powers were not adequately included in the core of global economic discussion and governance. Additionally, G20 summits of heads of state or government were held.

After the 2008 debut summit in Washington, DC, G20 leaders met twice a year: in London and Pittsburgh in 2009, and in Toronto and Seoul in 2010.

Since 2011, when France chaired and hosted the G20, the summits have been held only once a year. The 2016 summit was held in Hangzhou, China, the 2017 summit was held in Hamburg, Germany, the 2018 summit was held in Buenos Aires, Argentina, the 2019 summit was held in Osaka, Japan, the 2020 summit was scheduled in Riyadh, Saudi Arabia but it was held virtually due to COVID-19, the 2021 summit was held in Rome, Italy, the 2022 summit was held in Bali, Indonesia, the 2023 summit was held in New Delhi, India, the 2024 summit was held in Rio de Janeiro, Brazil, and the 2025 summit was held in Johannesburg, South Africa.

The 2026 summit will be held in Miami in the United States., and the 2027 event will travel to Manchester, UK.

To ensure continuity, the presidency is supported by a "troika" made up of the current, immediate past and next host countries.