The Chinook salmon /ʃɪˈnʊk/ (Oncorhynchus tshawytscha) is the largest and most valuable species of Pacific salmon. Its common name is derived from the Chinookan peoples. Other vernacular names for the species include king salmon, quinnat salmon, spring salmon, blackmouth, and tyee salmon. The scientific species name is based on the Russian common name chavycha (чавыча).

Chinook are anadromous fish native to the North Pacific Ocean and the river systems of western North America, ranging from California to Alaska, as well as Asian rivers ranging from northern Japan to the Palyavaam River in Arctic northeast Siberia. They have been introduced to other parts of the world, including New Zealand and Patagonia. Introduced Chinook salmon are thriving in Lake Michigan and Michigan's western rivers. A large Chinook is a prized and sought-after catch for a sporting angler. The flesh of the salmon is also highly valued for its dietary nutritional content, which includes high levels of important omega-3 fatty acids. Some populations are endangered; however, many are healthy. The Chinook salmon has not been assessed for the IUCN Red List. According to NOAA, the Chinook salmon population along the California coast is declining from factors such as overfishing, loss of freshwater and estuarine habitat, hydropower development, poor ocean conditions, and hatchery practices.

Historically, the native distribution of Chinook salmon in North America ranged from the Ventura River in California in the south to Kotzebue Sound in Alaska in the north. Recent studies have shown that Chinook salmon are historically native to the Guadalupe River watershed in California, the southernmost major metropolitan area hosting salmon runs in the United States. Populations have disappeared from large areas where they once flourished, however, or shrunk by as much as 40 percent. In some regions, their inland range has been cut off, mainly by dams and habitat alterations: in Southern California, in some areas east of the Coast Ranges of California and Oregon, and in large areas in the Snake River and upper Columbia River drainage basins. In certain areas such as California's Sacramento–San Joaquin River Delta, it was revealed that extremely low numbers of juvenile Chinook salmon (less than 1%) were surviving.

In the western Pacific, the distribution ranges from northern Japan (Hokkaido) in the south to the Arctic Ocean as far as the East Siberian Sea and Palyavaam River in the north. Nevertheless, they are consistently present and the distribution is well known only in Kamchatka. Elsewhere, information is scarce, but they have a patchy presence in the Anadyr River basin and parts of the Chukchi Peninsula. Also, in parts of the northern Magadan Oblast near the Shelikhov Gulf and Penzhina Bay, stocks might persist but remain poorly studied.

In 1967, the Michigan Department of Natural Resources introduced Chinook into Lake Michigan and Lake Huron to control the alewife, an invasive species of nuisance fish from the Atlantic Ocean. In the 1960s, alewives constituted 90% of the biota in these lakes. Coho salmon had been introduced the year before, and the program was successful. Chinook and Coho salmon thrived on the alewives and spawned in the lakes' tributaries. After this success, Chinook were introduced into the other Great Lakes, where sport fishermen prize them for their aggressive behaviour on the hook.^{[citation needed]} Despite a consistent program of release, the chinook has not established itself as a natively reproducing species in the Great Lakes. While limited natural reproduction occurs in the wild, the continued presence of the fish is depended on yearly stocking.

The species has also established itself in Patagonian waters in South America, where both introduced and escaped hatchery fish have colonized rivers and established stable spawning runs. Chinook salmon have been found spawning in headwater reaches of the Rio Santa Cruz, apparently having migrated over 1,000 km (620 mi) from the ocean. The population is thought to be derived from a single stocking of juveniles in the lower river around 1930.

Sporadic efforts to introduce the fish to New Zealand waters in the late 19th century were largely failures and led to no evident establishments. Initially ova were imported from the Baird hatchery of the McCloud River in California. Further efforts in the early 20th century were more successful and subsequently led to the establishment of spawning runs in the rivers of Canterbury and North Otago: Rangitata River, the Ōpihi River, the Ashburton River, the Rakaia River, the Waimakariri River, the Hurunui River, and the Waiau Uwha River. The success of the latter introductions is thought to be partly attributable to the use of ova from autumn-run populations as opposed to ova from spring-run populations used in the first attempts. Whilst other salmon have also been introduced into New Zealand, only Chinook salmon (or king salmon as it is known locally in New Zealand) have established sizeable pelagic runs.

The Chinook is blue-green, red, or purple on the back and on the top of the head, with silvery sides and white ventral surfaces. It has black spots on its tail and the upper half of its body. Although spots are seen on the tail in pink salmon and silver on the tail in coho and chum salmon, Chinook are unique among the Pacific salmon in combining black spots and silver on the tail. Another distinctive feature is a black gum line that is present in both salt and fresh water. Adult fish typically range in size from 60 to 90 cm (24 to 36 in), but may be up to 150 cm (58 in) in length; they average 4.5 to 22.7 kg (10 to 50 lb), but may reach 59 kg (130 lb). The meat can be either pink or white, depending on what the salmon have been feeding on.