Toronto is the largest city in Canada and the provincial capital of Ontario. It is located in Southern Ontario on the northwestern shore of Lake Ontario. With over 2.5 million residents, it is the fifth most populous municipality in North America. Toronto is at the heart of the Greater Toronto Area (GTA), and is part of a densely populated region in Southern Ontario known as the Golden Horseshoe, which is home to over 8.1 million residents—approximately 25% of Canada's population. The census metropolitan area (CMA) had a population of 5,113,149, and the Greater Toronto Area had a population of 5,555,912 in the 2006 Census.

As Canada's economic capital, Toronto is considered a global city and is one of the top financial centres in the world. Toronto's leading economic sectors include finance, business services, telecommunications, aerospace, transportation, media, arts, film, television production, publishing, software production, medical research, education, tourism and sports industries. The Toronto Stock Exchange, the world's eighth largest in terms of market value, is headquartered in the city, along with most of Canada's corporations.

Toronto's population is cosmopolitan and international, reflecting its role as an important destination for immigrants to Canada. Toronto is one of the world's most diverse cities by percentage of non-native-born residents, as about 49% of the population were born outside of Canada. Because of the city's low crime rates, clean environment, high standard of living, and friendly attitude to diversity, Toronto is consistently rated as one of the world's most livable cities by the Economist Intelligence Unit and the Mercer Quality of Living Survey. In addition, Toronto was ranked as the most expensive Canadian city in which to live in 2006. Residents of Toronto are called Torontonians.

The many residential communities of Toronto express a character distinct from that of the skyscrapers in the commercial core. Victorian and Edwardian-era residential buildings can be found in enclaves such as Rosedale, Cabbagetown, The Annex, and Yorkville. Wychwood Park is historically significant for the architecture of its homes, and for being one of Toronto's earliest planned communities. The Wychwood Park neighbourhood was designated as an Ontario Heritage Conservation district in 1985. The Casa Loma neighbourhood is named after Casa Loma, a storybook castle built in 1911 complete with stunning gardens, multiple turrets, massive stables, an elevator, secret passages, and bowling alleys. Spadina House is a 19th century manor that is now a museum.

The City of Toronto encompasses a geographical area formerly administered by six separate municipalities. These municipalities have each developed a distinct history and identity over the years, and their names remain in common use among Torontonians. Throughout the city there exist hundreds of small neighbourhoods and some larger neighbourhoods covering a few square kilometres. Former municipalities include East York, Etobicoke, North York, Old Toronto, Scarborough, and York.

The Old City of Toronto covers the area generally known as downtown. It is the historic core of Toronto and remains the most densely populated part of the city. The Financial District contains the largest cluster of skyscrapers in Canada, including the First Canadian Place, Toronto Dominion Centre, Scotia Plaza, Royal Bank Plaza, Commerce Court and Brookfield Place. From that point, the Toronto skyline extends northward along Yonge Street. Old Toronto is also home to many historically wealthy residential enclaves, such as Yorkville, Rosedale, The Annex, Forest Hill, Lawrence Park, Lytton Park, Moore Park, and Casa Loma, most stretching away from downtown to the north. These neighbourhoods generally feature upscale homes, luxury condominiums and high-end retail. At the same time, the downtown core vicinity includes neighbourhoods with many recent immigrants and low-income families living in social housing and rental high-rises, such as St. James Town, Regent Park, Moss Park, Alexandra Park and Parkdale. East and west of Downtown, neighbourhoods such as Kensington Market, Leslieville, Cabbagetown and Riverdale are home to bustling commercial and cultural areas as well as vibrant communities of artists with studio lofts, with many middle and upper class professionals. Other neighbourhoods in the central city retain an ethnic identity, including two Chinatowns, the popular Greektown area, the trendy Little Italy, Portugal Village, and Little India, along with others.

The inner suburbs are contained within the former municipalities of York and East York. These are mature and traditionally working class areas, primarily consisting of post-World War I small, single-family homes and small apartment blocks. Neighbourhoods such as Crescent Town, Thorncliffe Park, Weston, and Oakwood-Vaughan mainly consist of high-rise apartments, which are home to many new immigrant families. Recently, many neighbourhoods have become ethnically diverse and have undergone gentrification, as a result of increasing population and a housing boom during the late 1990s and 2000s. The first neighbourhoods affected were Leaside and North Toronto, gradually progressing into the western neighbourhoods in York. Some of the area's housing is in the process of being replaced or remodelled.

The outer suburbs comprising the former municipalities of Etobicoke (west), Scarborough (east) and North York (north) largely retain the grid plan laid before post-war development. Sections were long established and quickly growing towns before the suburban housing boom began and the emergence of Metro Government, existing towns or villages such as Mimico, Islington and New Toronto in Etobicoke; Willowdale, Newtonbrook and Downsview in North York; Agincourt, Wexford and West Hill in Scarborough where suburban development boomed around or between these and other towns beginning in the late 1940s. Upscale neighbourhoods were built such as the Bridle Path in North York, the area surrounding the Scarborough Bluffs in Guildwood, and most of central Etobicoke, such as Humber Valley Village, and The Kingsway. One of largest and earliest "planned communities" was Don Mills, parts of which were first built in the 1950s.[40] Phased development mixing single-detached housing with higher density apartment blocks became more popular as a suburban model of development. To some this model has been copied in other GTA municipalities surrounding Toronto, albeit with less population density. Over the last few decades, the North York Centre that runs along Yonge Street and the Scarborough City Centre have emerged as secondary business centres outside the downtown core. High-rise development in these areas have given North York and Scarborough distinguishable skylines of their own and a more downtown feel with high-density transit corridors serving them.