The Trans Canada Highway is officially the longest national highway in the world. It is not a single road, however, but consists of a half dozen different routes that traverse the country, stretching from the Pacific Ocean in the West to the Atlantic Ocean in the East and crossing 10 Canadian provinces.

The primary route starts in Victoria, British Columbia on the Pacific, and ends up in St. John's, Newfoundland on the Atlantic, with a length of 7604 km (4753 miles).

From Mile 0 in Victoria, the highway runs along route 1 in British Columbia for 986 km (616 miles), including a 30 km ferry trip from Nanaimo on Vancouver Island to Horseshoe Bay on the mainland. In BC, the highway passes through Vancouver and Kamloops. At Lake Louise, the highway enters Alberta, where it runs along route 1 for 524 km (326 miles), pasing through Calgary and Medecine Hat. At Walsh, the Trans Canada enters the province of Saskatchewan, running along route 1 for 655 km (407 miles). After passing through Moose Jaw and Regina, it enters Manitoba at Fleming. The cities of Brandon. Portage La Prairie and Winnipeg are on the Trans Canada (as route 1), before entering Ontario 497 km (309 miles) later, at West Hawk Lake. The main branch of the Trans Canada runs along Ontario route 17 as far as Sudbury, after passing through Kenora, Thunder Bay and Sault Sainte Marie. There, it runs along route 69 to Waubaushene, splits off onto route 12 for about 90 km, and then lies along route 7 through Peterbrorough to the capital of Canada, Ottawa. From there, it once again runs along route 17 to the Québec border. The total distance in Ontario is 2348 km (1468 miles). Once in Québec, the highway runs along route A40 (A for Autoroute, or freeway) to Montréal, jumps to the A25, and the A20 past Québec City to Rivière du Loup, where it follows route 185 to New Brunswick. The total distance spent in Québec is 573 km (358 miles). In New Brunswick, the Trans Canada follows route 2 past Fredericton to the Nova Scotia border at Amherst, 644 km (403 miles) away. Once in Nova Scotia, the highway is route 104 past Truro to the Canso Causeway, where it crosses over to Cape Breton Island and becomes route 105 to North Sydney, after 483 km (302 miles). From North Sydney, a 161 km (100 mile) ferry route lands at Port aux Basques in Newfoundland. 927 km (579 miles) further along route 1 is St. Johns, the Eastern endpoint of the Trans Canada Highway.

Several spurs exist. From West to East, the Yellowhead Highway runs as route 16 from Masset in BC on the Queen Charlotte Islands, via Prince Rupert, Edmonton Alberta and Saskatoon Saskatchewan to meet with route 1 at a point 13 km West of Portage la Prairie in Manitoba. The International Falls route splits off from Kenora in Northern Ontario, and runs along routes 71 and 11 via International Falls, to meet back up with the main route just west of Thunder Bay. The Northern Route follows route 11, leaving the main route at Nipigon in Northern Ontario, to Kirkland Lake, turning East along route 66, entering Québec as route 117 and continuing pas Val d'Or to Sainte Agathe where it follows route A15 to Montréal. Ontario route 17 from Sudbury to North Bay and Ottawa, and route 11 from Kirkland Lake to North Bay, are also designated as the Trans Canada. Finally, a spur leaves the main route in Eastern New Brunswick as route 16, and crosses the Confederation Bridge over the Northumberland Strait into Prince Edward Island and loops along 117 km (73 miles) of route 1 through Charlottetown to cross a ferry back from High Bank to Caribou in Nova Scotia. There it follows route 106 to join the main route at New Glasgow.

The Trans Canada Highway was commissioned in 1949 with the issue of the Trans Canada Highway Act as a post-WWII national unification project. Even though one of the conditions for British Columbia's joining the Canadian Confederation in 1871 was a road link to Eastern Canada, the link had so far not materialized. A railway did cross the country, but it was impossible to get from one end of canada to the other by road. Specifically, there was no road to the north of Lake Superior, and travellers had to go through the United States to the south. Similarly, road links over much of the Rocky Mountains were very poor, and again the US road system offered a more passable route.

Although the Trans Canada Highway was formally opened and dedicated in a ceremony at Rogers Pass in British Columbia on September 3, 1962, the primary route was still missing a 320 km section in Newfoundland, which was completed in 1965. The spurs mentioned above were added at later dates, with the Yellowhead being the most recent in 1986.

The Trans Canada Highway Act dictates the standards for any highways that are part of the national highway system. Specifically, all roads must be paved, and have at least two lanes. Lanes must be a minimum of 24 feet wide, and shoulders (either gravel or paved) must be at least 10 feet wide. The maximum allowable grade is six percent, curves must be less than three degrees, and stopping sight distance must be at least 600 feet. The first province to complete their section of the Highway was Saskatchewan, in 1957.

Recommended route signage for the Trans Canada is a green rectangle, of dimensions 5:3 (aligned vertically). A white band across the top should have the words "TRANS CANADA" written in green in a clearly legible font, and a white ribbon emblem across the bottom should have the name of the province written on it in green. A large white maple leaf emblem should occupy the center of the sign, and the route number should be clearly printed in a large green font in the center of the maple leaf. A placard immediately underneath may have the designation "EAST" or "WEST", as appropriate. French may be substituted for English for any of the written text. In some provinces, you will find this sign without a route number accompanying a similarly sized sign indicating the route number, as conforms to the provincial designation for such signage.