The Fraser River (/ˈfreɪzər/) is the longest river within British Columbia, Canada, rising at Fraser Pass near Blackrock Mountain in the Rocky Mountains and flowing for 1,375 kilometres (854 mi), into the Strait of Georgia just south of the City of Vancouver. The river's annual discharge at its mouth is 112 cubic kilometres (27 cu mi) or 3,550 cubic metres per second (125,000 cu ft/s), and each year it discharges about 20 million tons of sediment into the ocean.

The river is named after Simon Fraser, who led an expedition in 1808 on behalf of the North West Company from the site of present-day Prince George almost to the mouth of the river. The river's name in the Halqemeylem (Upriver Halkomelem) language is Sto:lo, often seen archaically as Staulo, and has been adopted by the Halkomelem-speaking peoples of the Lower Mainland as their collective name, Sto:lo. The river's name in the Dakelh language is Lhtakoh. The Tsilhqot'in name for the river, not dissimilar to the Dakelh name, is ʔElhdaqox, meaning Sturgeon (ʔElhda-chugh) River (Yeqox).

The Fraser drains a 220,000-square-kilometre (85,000 sq mi) area. Its source is a dripping spring at Fraser Pass in the Canadian Rocky Mountains near the border with Alberta. The river then flows north to the Yellowhead Highway and west past Mount Robson to the Rocky Mountain Trench and the Robson Valley near Valemount. After running northwest past 54° north, it makes a sharp turn to the south at Giscome Portage, meeting the Nechako River at the city of Prince George, then continues south, progressively cutting deeper into the Fraser Plateau to form the Fraser Canyon from roughly the confluence of the Chilcotin River, near the city of Williams Lake, southwards. It is joined by the Bridge and Seton Rivers at the town of Lillooet, then by the Thompson River at Lytton, where it proceeds south until it is approximately 64 kilometres (40 mi) north of the 49th parallel, which is Canada's border with the United States.

From Lytton southwards it runs through a progressively deeper canyon between the Lillooet Ranges of the Coast Mountains on its west and the Cascade Range on its east. Hell's Gate, located immediately downstream of the town of Boston Bar, is a famous portion of the canyon where the walls narrow dramatically, forcing the entire volume of the river through a gap only 35 metres (115 feet) wide. An aerial tramway takes visitors out over the river. Hells Gate is visible from Trans-Canada Highway 1 about 2 km (1.2 mi) south of the tramway. Simon Fraser was forced to portage the gorge on his trip through the canyon in June 1808.

At Yale, at the head of navigation on the river, the canyon opens up and the river widens, though without much adjoining lowland until Hope, where the river then turns west and southwest into the Fraser Valley, a lush lowland valley, and runs past Chilliwack and the confluence of the Harrison and Sumas Rivers, bending northwest at Abbotsford and Mission.

The Fraser then flows past Maple Ridge, Pitt Meadows, Port Coquitlam, and north Surrey. It turns southwest again just east of New Westminster, where it splits into the North Arm, which is the southern boundary of the City of Vancouver, and the South Arm, which divides the City of Richmond from the City of Delta to the south. Richmond is on the largest island in the Fraser, Lulu Island and also on Sea Island, which is the location of Vancouver International Airport, where the Middle Arm branches off to the south from the North Arm. The far eastern end of Lulu Island is named Queensborough and is part of the City of New Westminster. Also in the lowermost Fraser, among other smaller islands, is Annacis Island, an important industrial and port area, which lies to the southeast of the eastern end of Lulu Island. Other notable islands in the lower Fraser are Barnston Island, Matsqui Island, Nicomen Island and Sea Bird Island. Other islands lie on the outer side of the estuary, most notably Westham Island, a wildfowl preserve, and Iona Island, the location of the main sewage plant for the City of Vancouver.

The Fraser's delta empties into the Strait of Georgia between the mainland and Vancouver Island; the lands south of the City of Vancouver, including the cities of Richmond and Delta, sit on the flat flood plain. The islands of the delta include Iona Island, Sea Island, Lulu Island, Annacis Island, and a number of smaller islands. While the vast majority of the river's drainage basin lies within British Columbia, a small portion in the drainage basin lies across the international border in Washington in the United States, namely the upper reaches of the tributary Chilliwack and Sumas rivers. Most of lowland Whatcom County, Washington is part of the Fraser Lowland and was formed also by sediment deposited from the Fraser, though most of the county is not in the Fraser drainage basin.

Similar to the Columbia River Gorge east of Portland, Oregon, the Fraser exploits a topographic cleft between two mountain ranges separating a more continental climate (in this case, that of the British Columbia Interior) from a milder climate near the coast. When an Arctic high-pressure area moves into the British Columbia Interior and a relatively low-pressure area builds over the general Puget Sound and Strait of Georgia region, the cold Arctic air accelerates southwest through the Fraser Canyon. These outflow winds can gust up to 97 to 129 kilometres per hour (60 to 80 mph) and have at times exceeded 160 kilometres per hour (100 mph). Such winds frequently reach Bellingham and the San Juan Islands, gaining strength over the open water of the Strait of Juan de Fuca.