Alaska Day is a legal holiday in the U.S. state of Alaska, observed on October 18. It is the anniversary of the formal transfer of the Territory of Alaska from Russia to the United States which took place at a flag-raising ceremony at Fort Sitka on Friday October 18, 1867 (11 hours behind St. Petersburg, Russia, half past midnight, Saturday 7 October, St. Petersburg time, Julian Calendar, or 3:30 p.m. in Sitka, 7 October).

Alaska Day is observed statewide, and is a paid holiday for State of Alaska employees. The official celebration is held in Sitka, where schools release students early, many businesses close for the day, and events such as a parade and reenactment of the flag raising are held.

It should not be confused with Seward's Day, the last Monday in March which marks the signing of the treaty for the Alaska Purchase in which the U.S. purchased Alaska from Russia on March 30, 1867.

Although the territory was sold to the U.S. in March, it was not until the 18th of October that year that the Commissioners arrived in Sitka and the formal transfer was arranged. The original ceremony included 250 uniformed U.S. soldiers, who marched to the Governor's house in Sitka at "Castle Hill", where the transfer was made. It was here that the Russian troops lowered the Russian flag and the U.S. flag was raised.

Alaska (ⁱ/əˈlæskə/) is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait. Alaska is the 4th least populous and the least densely populated of the 50 United States. Approximately half of Alaska's 722,718 residents live within the Anchorage metropolitan area.

Alaska was purchased from Russia on March 30, 1867, for $7.2 million ($120 million in today's^[when?] dollars) at approximately two cents per acre ($4.74/km²). The land went through several administrative changes before becoming an organized (or incorporated) territory on May 11, 1912, and the 49th state of the U.S. on January 3, 1959.

The name "Alaska" (Аляска) was already introduced in the Russian colonial period, when it was used only for the peninsula and is derived from the Aleut alaxsxaq, meaning "the mainland" or, more literally, "the object towards which the action of the sea is directed". It is also known as Alyeska, the "great land", an Aleut word derived from the same root.