The Gulf of Alaska (Tlingit: Yéil T'ooch’) is an arm of the Pacific Ocean defined by the curve of the southern coast of Alaska, stretching from the Alaska Peninsula and Kodiak Island in the west to the Alexander Archipelago in the east, where Glacier Bay and the Inside Passage are found.

The Gulf shoreline is a combination of forest, mountain and a number of tidewater glaciers. Alaska's largest glaciers, the Malaspina Glacier and Bering Glacier, spill out onto the coastal line along the Gulf of Alaska. The coast is heavily indented with Cook Inlet and Prince William Sound, the two largest connected bodies of water. It includes Yakutat Bay and Cross Sound. Lituya Bay (a fjord north of Cross Sound, and south of Mount Fairweather) is the site of the largest recorded tsunami in history. It serves as a sheltered anchorage for fishing boats.

of Alaska is considered a Class I, productive ecosystem with more than 300 grams of carbon per square meter per year based on SeaWiFS data.

Deep water corals can be found in the Gulf of Alaska. Primnoa pacifica has contributed to the location being labeled as Habitat Areas of Particular Concern. P. pacifica is a deep water coral typically found between 150 metres (490 ft) and 900 metres (3,000 ft) here.

Thanks to Gulf Stream, while the Okhotsk Sea was "closed by ice in winter", just 10° further north, the "Gulf of Alaska was ice-free throughout the year". In 1977, the Gulf of Alaska started to manifest an unexpected and at that time inexplicable shift on its normal climate regime, resulting in a growth of the mean temperature of the sea surface and in an increased availability and variety of commercial fish species. A similar volatile climate change was observed during the 1970s in the North Pacific seas.