The 2010 G20 Toronto summit was the fourth meeting of the G20 heads of state/government, to discuss the global financial system and the world economy, which took place at the Metro Toronto Convention Centre in Toronto, Ontario, Canada. The summit's priorities included evaluating the progress of financial reform, developing sustainable stimulus measures, debating global bank tax, and promoting open markets. Alongside the twenty-one representatives of the G20 major economies, leaders of six invited nations, and eight additional intergovernmental organizations also took part in the summit.

Prior to the summit, Canadian Prime Minister Stephen Harper announced that the theme would be "recovery and new beginnings," referring to an anticipated economic stimulus from the impact of the ongoing world recession. Harper initially proposed to hold the summit in Huntsville, Ontario, where the 36th G8 summit was scheduled immediately prior. Organizers later deemed the town insufficient to provide hospitality for the large number of G20 delegates and journalists, favouring Toronto as the host location.

Organizers formed an Integrated Security Unit, consisting of police officers from several regional departments, to provide security during the summit in Downtown Toronto. The event was part of the largest and most expensive security operation in Canadian history. Many hundreds of members of the public were wrongfully detained, some held in inhumane conditions. The total combined cost between the 36th G8 summit in Huntsville and the G20 summit in Toronto including security, infrastructure, and hospitality, was determined to be approximately C$858 million.

Many leaders of the G20 disagreed about which issues should be discussed at the summit. The prime focus of the summit discussions was the recovery from the ongoing global recession and the European debt crisis. Summit leaders were divided over which strategies would be best for tackling these problems. The European Union emphasized the need to cut their deficits by focusing on austerity measures. In contrast, the United States emphasized the importance of maintaining economic stimulus spending in order to encourage growth. In summit discussions, the countries of the European Union explained projected reductions in spending and balanced budgets. Alternatively, China, India, and the United States argued in favor of increased stimulus funding to mitigate the effects of recession. Among the specifics proposed by the European Union were a global bank tax and a Robin Hood tax, but the United States and Canada opposed these plans. Other topics of concern were international development and continuing international aid to Africa and other developing nations. Some invitees expressed criticism of Israel's Gaza strip blockade and of the nuclear programs of North Korea and the United States raised issues of corruption and security in Afghanistan.

Security officials began preparing for summit security in Toronto in February 2010. General policing and patrolling was provided by the Toronto Police Service, the Ontario Provincial Police, the Royal Canadian Mounted Police, and the Canadian Forces, while the Peel Regional Police aided in policing at Toronto Pearson International Airport in Mississauga during the arrivals of delegates. The five departments formed an Integrated Security Unit (ISU), similar to the one created for the 2010 Winter Olympics in Vancouver. Additional officers were deployed from York Regional Police, Halton Regional Police Service, Barrie Police Service,Greater Sudbury Police Service, Waterloo Regional Police Service, Niagara Regional Police Service, Hamilton Police Service, Ottawa Police Service, and Service de police de la Ville de Montréal. Calgary Police Service supplied 150 volunteer police officers a week before the summit.

According to an early estimate by The Globe and Mail, 25,000 uniformed police officers, 1,000 security guards from Commissionaires Great Lakes, and several Canadian military forces were to be deployed during the summit. The North American Aerospace Defense Command (NORAD) conducted Amalgam Virgo exercises on May 6 and 7 across the Greater Toronto Area using CF-18 Hornet jets, CH-124 Sea Kings, and CH-146 Griffon helicopters at low altitudes. The total cost for security at both the G8 and the G20 summits was determined to be $1.8 billion, paid entirely by the federal Crown-in-Council, excluding the costs of any possible damage to local business.

The ISU created a security perimeter, beginning with the outer boundary, specifically bordered by King Street to the north, Lake Shore Boulevard to the south, Yonge Street to the east, and Spadina Avenue to the west, where vehicles would be restricted during the summit dates. Residents who lived within the security zone were issued registration cards prior to the summit and other pedestrians who wished to enter the security zone were only able to do so at one of 38 checkpoints, where they were required to present two pieces of photo identification and provide justification for entry. The area surrounding the Metro Toronto Convention Centre itself was fenced and off-limits to civilians and protesters. The 3-metre (10 ft) high fence, contracted to SNC-Lavalin by Public Works and Government Services Canada and installed by two Gormley, Ontario-based companies, was built at a cost of $5.5-million and installation began on June 7. The Toronto Police Service installed 77 additional closed-circuit television security cameras in the area and purchased four Long Range Acoustic Devices which were to be in use exclusively during the summit. The ISU decided on also using water cannons for riot control. The security perimeter even extended into the waters of Lake Ontario and included a Maritime Security Operation with numerous Police vessels and the Canadian Coast Guard Ship Griffon patrolling to discourage international demonstrators from unlawful entry into Canada.

A former film studio located on Eastern Avenue was designated as a temporary detention centre for individuals arrested during the summit. Toronto Police Service announced that Trinity Bellwoods Park would be the designated protest area, but following opposition from local residents, police relocated the designated protest zone to the northern part of Queen's Park. Canada Post declared that it would remove post boxes in the security zone. Toronto Parking Authority removed some parking meters as well. Small trees along sidewalks around the convention centre were removed to prevent them from being used as weapons by protesters. Other removed municipal properties include 745 newspaper boxes, 200 public trash cans, 70 mailboxes, 29 bus shelters, and 5 public information boards.