The Aleutian Islands (possibly from Chukchi aliat, "island") are a chain of more than 300 small volcanic islands forming an island arc in the Northern Pacific Ocean, occupying an area of 6,821 sq mi (17,666 km²) and extending about 1,200 mi (1,900 km) westward from the Alaska Peninsula toward the Kamchatka Peninsula. Crossing longitude 180°, they are the westernmost part of the United States (and technically also the easternmost; see Extreme points 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 Komandorski 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 are part of the larger Pacific Mountain System physiographic division.