The Queen Elizabeth Way (QEW) is a 400-series highway in the Canadian province of Ontario linking Toronto with the Niagara Peninsula and Buffalo, New York. The freeway begins at the Peace Bridge in Fort Erie and travels 139.1 kilometres (86.4 mi) around the western end of Lake Ontario, ending at Highway 427 as the physical highway continues as the Gardiner Expressway into downtown Toronto. The QEW is one of Ontario's busiest highways, with an average of close to 200,000 vehicles per day on some sections. Major highway junctions are at Highway 420 in Niagara Falls, Highway 405 in Niagara-on-the-Lake, Highway 406 in St. Catharines, the Red Hill Valley Parkway in Hamilton, Highway 403 and Highway 407 in Burlington, Highway 403 at the Oakville–Mississauga boundary, and Highway 427 in Etobicoke. Within the Regional Municipality of Halton the QEW is signed concurrently with Highway 403. The speed limit is 100 km/h (62 mph) throughout most of its length, with the exceptions being between Hamilton and St. Catharines where the posted limit is 110 km/h (68 mph).

The 400-series highways are a network of controlled-access highways in the Canadian province of Ontario, forming a special subset of the provincial highway system. They are analogous to the Interstate Highway System in the United States or the Autoroute system of neighbouring Quebec, and are regulated by the Ministry of Transportation of Ontario (MTO). The 400-series designations were introduced in 1952, although Ontario had been constructing divided highways for two decades prior. Initially, only Highways 400, 401 and 402 were numbered; other designations followed in the subsequent decades. The network is situated almost entirely in Southern Ontario, although Highway 400 extends into the more remote northern portion of the province.