Bounded north and south by water, Ontario is Canada's most populous and most industrialized province. Second in size, it covers an area larger than France and Spain combined. Ninety percent of the population lives on less than 15 percent of the land—in the fertile St. Lawrence lowlands and in the "golden horseshoe" stretching from Oshawa to the Niagara peninsula. The St. Lawrence Seaway, one of the world's busiest shipping lanes, gives oceangoing vessels access to the interior of North America.

As Canada's heartland, Ontario contributes more than 40 percent of the gross domestic product. Automobiles are manufactured in cities such as Oshawa, Windsor, and St. Thomas. Newsprint is the principal wood product; about a fifth of Canada's pulp and paper issues from the seemingly endless expanse of conifers that clothe the northern areas of the province. Toronto—the main port of entry for Canada's immigrants—ranks also as the nation's chief publishing, commercial, and banking center.

Hydroelectricity is a power train between the resource-rich north and the industrially energetic south. The Ottawa, Niagara, and St. Lawrence Rivers are major sources of hydroelectric power, but Ontario Hydro's network of nuclear power stations now produces close to half the province's electricity. The provincial government owns some nine-tenths of the forest lands and grants logging licenses to private companies. Public debate raises questions about the future of the boreal forests.