The Aleutian Islands are a chain of 14 large volcanic islands and 55 smaller ones belonging to both the United States and Russia. They form part of the Aleutian Arc in the Northern Pacific Ocean, occupying an area of 6,821 square miles (17,666 km2) and extending about 1,200 miles (1,900 km) westward from the Alaska Peninsula toward the Kamchatka Peninsula in Russia, and mark a dividing line between the Bering Sea to the north and the Pacific Ocean to the south. While nearly all the archipelago is part of Alaska and is usually considered as being in the "Alaskan Bush", at the extreme western end, the small, geologically related Commander Islands belong to Russia.
The islands, with their 57 volcanoes, are in the northern part of the Pacific Ring of Fire. Physiographically, they are a distinct section of the larger Pacific Border province, which in turn is part of the larger Pacific Mountain System physiographic division.