Autoroute 20 is a Quebec Autoroute, following the Saint Lawrence River through one of the more densely populated parts of Canada, with its central section forming the main route of the Trans-Canada Highway from the A-25 interchange to the A-85 interchange. At 585 km (363.5 mi), it is the longest Autoroute in Quebec. It is one of two main links between Montreal and Quebec City; the other is the A-40.

The Quebec Autoroute System or le système d'autoroute au Québec is a network of freeways within the province of Quebec, Canada, operating under the same principle of controlled access as the Interstate Highway System in the United States and the 400-series highways in neighbouring Ontario. The Autoroutes are the backbone of Quebec's highway system, spanning almost 2,400 km (1,491 mi). The speed limit on the Autoroutes is generally 100 km/h (62 mph) in rural areas and 70–90 km/h (43–56 mph) in urban areas; most roads are made of asphalt concrete.