Ottawa ( /ˈɒtəwə/ (help·info) or sometimes /ˈɒtəwɑː/) is the capital of Canada and a municipality within the Province of Ontario. Located in the Ottawa Valley in the eastern portion of Southern Ontario, the city lies on the southern banks of the Ottawa River, a major waterway forming the local boundary between the Provinces of Ontario and Quebec.

Connected by several bridges to its Quebec neighbour, the city of Gatineau on the northern shores of the Ottawa River, the two cities and surrounding areas are designated the National Capital Region (NCR). Though governed by separate municipal governments, the federal lands within the region are administered by the National Capital Commission (NCC), a federal crown corporation charged with the responsibility of planning and managing the federal government's interests in the NCR.

In 2006, the city of Ottawa had a population of 812,129, making it the fourth-largest municipality in the country and second-largest in Ontario. The Ottawa-Gatineau metropolitan area had a 2006 population of 1,130,761, making it the fourth-largest census metropolitan area (CMA) in Canada. The National Capital Region which encompasses Ottawa, Gatineau and surrounding suburbs and towns has an estimated population of 1,451,415. In 2009 Ottawa-Gatineau's population was estimated at 1,220,674, making it the fifth-largest CMA in Canada. Ottawa is also considered the 4th cleanest city in the world by Forbes magazine.

As with other national capitals, the word "Ottawa" is also used to refer by metonymy to the country's federal government, especially as opposed to provincial or municipal authorities.