Mississauga ( (listen) MISS-ih-SAW-gə), historically known as Toronto Township, is a city in the Canadian province of Ontario. It is situated on the shores of Lake Ontario in the Regional Municipality of Peel, adjoining the western border of Toronto. With a population of 717,961 as of 2021, Mississauga is the seventh-most populous municipality in Canada, third-most in Ontario, and second-most in the Greater Toronto Area (GTA) after Toronto itself. However, for the first time in its history, the city's population declined according to the 2021 census, from a 2016 population of 721,599 to 717,961, a 0.5 percent decrease.

The growth of Mississauga was attributed to its proximity to Toronto. During the latter half of the 20th century, the city attracted a multicultural population and built up a thriving central business district. Malton, a neighbourhood of the city located in its northeast end, is home to Toronto Pearson International Airport, Canada's busiest airport, as well as the headquarters of many Canadian and multinational corporations. Mississauga is not a traditional city, but is instead an amalgamation of three former villages, two townships, and a number of rural hamlets (a general pattern common to several suburban GTA cities) that were significant population centres, with none being clearly dominant, prior to the city's incorporation that later coalesced into a single urban area.

Indigenous people have lived in the area for thousands of years and Mississauga is situated on the traditional territory of the Huron-Wendat, Haudenosaunee and Anishinaabeg people, including the namesake Mississaugas. Most of present-day Mississauga was founded in 1805 as Toronto Township within York County, and became part of Peel County when new counties were formed by splitting off parts of the original county in 1851. Mississauga itself was established in 1968 as a town, and was reincorporated as a city in 1974, when Peel was restructured into a regional municipality.