Aleut (/ˈæliuːt/ AL-ee-oot) or Unangam Tunuu is the language spoken by the Aleut living in the Aleutian Islands, Pribilof Islands, Commander Islands, and the Alaska Peninsula (in Aleut Alaxsxa, the origin of the state name Alaska). Aleut is the sole language in the Aleut branch of the Eskimo–Aleut language family. The Aleut language consists of three dialects, including Unalaska (Eastern Aleut), Atka/Atkan (Atka Aleut), and Attu/Attuan (Western Aleut, now extinct).

Various sources estimate there are fewer than 100 to 150 remaining active Aleut speakers. Because of this, Eastern and Atkan Aleut are classified as "critically endangered and extinct" and have an Expanded Graded Intergenerational Disruption Scale (EGIDS) rating of 7. The task of revitalizing Aleut has largely been left to local government and community organizations. The overwhelming majority of schools in the historically Aleut-speaking regions lack any language/culture courses in their curriculum, and those that do fail to produce fluent or even proficient speakers.

The Eskimo and Aleut peoples were part of a migration from Asia across Beringia, the Bering land bridge between 4,000 and 6,000 years ago. During this period, the Proto-Eskimo-Aleut language was spoken, which broke up around 2000 BC. Differentiation of the two branches is thought to have happened in Alaska because of the linguistic diversity found in the Eskimo languages of Alaska relative to the entire geographic area where Eskimo languages are spoken (eastward through Canada to Greenland). After the split between the two branches, their development is thought to have occurred in relative isolation.

Evidence suggests a culture associated with Aleut speakers on the Eastern Aleutian Islands as early as 4,000 years ago, followed by a gradual expansion westward over the next 1,500 years to the Near Islands. Another westward expansion may have occurred about 1,000 years ago, which may explain the lack of obvious diversification among the Aleut dialects, with Eastern Aleut features having spread westward. This second westward expansion is characterized as a period of cultural affinity with southeastern Alaska and the Pacific Northwest Coast, which may explain linguistic features that Aleut shares with neighboring non-Eskimo languages, such as rules of plural formation.

Due to colonization by Russian colonizers and traders in the 18th and 19th centuries, Aleut has a large portion of Russian loanwords. However, they do not affect the basic vocabulary and thus do not suggest undue influence on the language.

In March 2021, the last native speaker of the Bering dialect, Vera Timoshenko, died aged 93 in Nikolskoye, Bering Island, Kamchatka.

Within the Eastern group are the dialects of the Alaskan Peninsula, Unalaska, Belkofski, Akutan, the Pribilof Islands, Kashega and Nikolski. The Pribilof dialect has more living speakers than any other dialect of Aleut.

The Atkan grouping comprises the dialects of Atka and Bering Island.