Alaska was purchased from the Russian Empire on March 30, 1867, for $7.2 million at about two cents per acre ($4.74/km²). The land went through several administrative changes before becoming an organized 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 time, 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.

Alaska has a longer coastline than all the other U.S. states combined. It is the only non-contiguous U.S. state on continental North America; about 500 miles (800 km) of British Columbia (Canada) separate Alaska from Washington state. Alaska is thus an exclave of the United States. It is technically part of the continental U.S., but is often not included in colloquial use; Alaska is not part of the contiguous U.S., often called "the Lower 48." The capital city, Juneau, is situated on the mainland of the North American continent, but is not connected by road to the rest of the North American highway system.

The state is bordered by the Yukon Territory and British Columbia in Canada, to the east, the Gulf of Alaska and the Pacific Ocean to the south, the Bering Sea, Bering Strait, and Chukchi Sea to the west and the Arctic Ocean to the north. Alaska's territorial waters touch Russia's territorial waters in the Bering Strait, as the Russian Big Diomede Island and Alaskan Little Diomede Island are only 3 miles (4.8 km) apart. As it extends into the eastern hemisphere, it is technically both the westernmost and easternmost state in the United States, as well as also being the northernmost.

Alaska is the largest state in the United States in land area at 586,412 square miles (1,518,800 km2), over twice the size of Texas, the next largest state. Alaska is larger than all but 18 sovereign countries. Without Alaska, Brazil and Australia are larger than the United States.

Counting territorial waters, Alaska is larger than the combined area of the next three largest states: Texas, California, and Montana. It is also larger than the combined area of the 22 smallest U.S. states.

The regions:

The International Date Line was drawn west of 180° to keep the whole state, and thus the entire North American continent, within the same legal day.

With its myriad islands, Alaska has nearly 34,000 miles (54,720 km) of tidal shoreline. The Aleutian Islands chain extends west from the southern tip of the Alaska Peninsula. Many active volcanoes are found in the Aleutians. Unimak Island, for example, is home to Mount Shishaldin, which is an occasionally smoldering volcano that rises to 10,000 feet (3,000 m) above the North Pacific. It is the most perfect volcanic cone on Earth, even more symmetrical than Japan's Mount Fuji. The chain of volcanoes extends to Mount Spurr, west of Anchorage on the mainland. Alaska has more volcanoes than any other state. Geologists have identified Alaska as part of Wrangellia, a large region consisting of multiple states and Canadian provinces in the Pacific Northwest which is actively undergoing continent building.

One of the world's largest tides occurs in Turnagain Arm, just south of Anchorage – tidal differences can be more than 35 feet (10.7 m). (Many sources say Turnagain has the second-greatest tides in North America, but several areas in Canada have larger tides.)