Who are the members of the G20?
The G20, or Group of 20, are leading industrialised and emerging powers that hold annual summits on economic governance and international issues and crises that affect the countries.
It is the main forum for international cooperation on matters of global finance and economy.
Members include the G7 (Group of Seven) countries, as well as Argentina, Australia, Brazil, Britain, Canada, France, Germany, Indonesia, Italy, Japan, Mexico, Saudi Arabia, South Africa, South Korea, Turkey and the European Union.
The G20 countries account for more than four-fifths of the world gross product and three-quarters of global trade.
Together, the countries also account for two-thirds of the world population.
The group is headed by a rotating presidency. Germany assumed the G20 Presidency on December 1, 2016.
Next year's G20 host will be Argentina.
Who attends the meetings?
Ministerial-level meetings began in 1999, in which the finance ministers and heads of central banks of member countries gathered for talks.
Meetings between the heads of state and government started with questions and concerns brought on by the 2008 global financial crisis. The 2008 crisis also broadened the G20 agenda.
The heads of global and regional bodies are invited to the summits, among them the chiefs of the UN, IMF, World Bank, WTO, African Union, APEC and Southeast Asia's ASEAN.
Rotating G20 summits also invite guest nations, including "permanent guest" Spain and, this year, partner countries the Netherlands, Norway and Singapore.
What happens at the meetings?
Although the G20 summit is known for the meeting of heads of state and government, there are several ministerial meetings between the finance, labour, foreign affairs, health and agriculture ministers of the member countries in the months leading to the summit. These meetings lay the groundwork for the final meeting at the summit.
Countries may also hold bilateral talks ahead of the summit.
Countries also hold dialogues and forums with civil society groups and leaders, and hold special sessions, including with trade unions and research organisations to prepare for the summit.
At the meeting of heads of state, the leaders mostly meet behind closed doors. The outcome of the discussions and negotiations are published in a Leaders' Communiqué.
Although the communiqué is not legally binding, it has political force.
What is this year's summit about?
The Summit of the Heads of State and Government will take place in Hamburg, Germany between July 7 and July 8 under the theme, "Shaping an Interconnected World."
The topics include issues of international importance related to economic and financial issues, like climate change, migration, terrorism and security.
Why do people protest it every year?
The grouping has often been a magnet for protesters who march against globalisation and what they say is corporate greed and a failure to tackle climate change.
This year, German authorities expect around 8,000 demonstrators, the interior minister said on Tuesday. Some 20,000 police officers will be deployed.
Hundreds of mainly young left-wing activists gathered and marched on a main street shortly before midnight on Tuesday in the first major protest ahead of the summit, which will be attended by US President Donald Trump, Russian President Vladimir Putin and Turkish President Recep Tayyip Erdogan.
At the 2010 summit in Toronto, thousands of anti-capitalist protesters clashed with Canadian police, leaving dozens injured on both sides and sparking mass arrests.