The Aleutian Islands are a chain of more than 300 small volcanic islands, forming part of the Aleutian Arc in the Northern Pacific Ocean, occupying an area of 17,666 square km and extending about 1,931 km westward from the Alaska Peninsula toward the Kamchatka Peninsula thus marking a line between the Bering Sea and the Pacific Gulf of Alaska. Crossing longitude 180°, they are the westernmost part of the United States. Nearly all the archipelago is part of Alaska and usually considered as being in the Alaskan Bush, but at the extreme western end the small, geologically-related, and remote Commander Islands are in Russia. The islands, with their 57 volcanoes, are in the northern part of the Pacific Ring of Fire. The Alaska Marine Highway passes through the islands.
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.