Yukon River, 3185 km long (of which 1149 km lie in Canada), fifth-longest river in North America, rises in Tagish Lake on the northern BC border, flows north and northwest across the Yukon Territory into Alaska, where it flows in a great westward arc to Norton Sound on the Bering Sea. It has a drainage area of about 800,000 km2 and an average discharge of 2300 m3/s where it crosses into Alaska.

Four principal tributaries, draining a vast area of the Yukon Territory, feed the river in Canada. The Teslin River (393 km) rises in Teslin Lake, on the BC border, and joins the Yukon north of Lake Laberge. The Pelly River (608 km) rises in the Selwyn Mountains to the east and descends to the Yukon at Fort Selkirk. The White River (320 km) drains the glacial waters of the southwest, and the Stewart River (644 km) rises in the mountainous area to the east, in the mining region of Mayo and Keno Hill. In Alaska the major tributaries are the Porcupine River (721 km), which rises in the northwest Yukon Territory, the Tanana from the south, and the Koyukuk from the north.

The Yukon is a slow-moving, braided stream, and is shallow except when swollen by spring waters. Its gradient is even and there are few rapids; those at Miles Canyon, which proved so treacherous to the Klondike prospectors, have been drowned by a hydroelectric development. From Fort Selkirk to Dawson, the river is sprinkled with wooded islands and its long, wide stretches are bordered by mountains. Past Dawson, the valley becomes narrow and then, as it enters Alaska, widens into the broad interior plateau called the "Yukon Flats."

The river mouth was known to Russian fur traders by 1831. The upper reaches were explored by HBC trader Robert Campbell, who explored the Pelly River and established a post at Fort Selkirk on the Yukon in 1848. John Bell of the HBC reached the river via the Porcupine River in 1846. For 3 months of the year, the Yukon is navigable from its mouth to Whitehorse (some 2860 km). Steamers plied the river in the 1860s, and there were at least 20 in service in 1900, at the height of the Klondike Gold Rush. Today the steamers are antique and the area is served by road and air.

The Yukon basin is believed to be the chief migration route of America's original settlers (see Prehistory). However, it remains sparsely populated. Several thousand native people maintain their traditional life-style, being at least partly dependent on hunting and trapping. The forest cover of small conifers supplies local needs, but growth is too slow for a viable forestry industry; there is little agriculture. The isolation and scenic beauty of the river attracts tourists. The name Yukon was first applied to the river and is from the Gwich'in word Yu-kun-ah, meaning "great river."