The Yakut language (/jəˈkuːt/ yə-KOOT), also known as the Sakha language (/səˈxɑː/ sə-KHAH) or Yakutian, is a Siberian Turkic language spoken by around 450,000 native speakers—primarily by ethnic Yakuts. It is one of the official languages of the Sakha Republic, a republic in the Russian Federation.

The Yakut language has a large number of loanwords of Mongolic origin, a layer of vocabulary of unclear origin, as well as numerous recent borrowings from Russian. Like other Turkic languages, Yakut is an agglutinative language and features vowel harmony.

Yakut is a member of the Northeastern Common Turkic family of languages, which also includes Shor, Tuvan and Dolgan. Like most Turkic languages, Yakut has vowel harmony, is agglutinative and has no grammatical gender. Word order is usually subject–object–verb. Yakut has been influenced by Tungusic and Mongolian languages.

Historically, Yakut left the community of Common Turkic speakers relatively early. Due to this, it diverges in many ways from other Turkic languages and mutual intelligibility between Yakut and other Turkic languages is low and many cognate words are hard to notice when heard. Nevertheless, Yakut contains many features which are important for the reconstruction of Proto-Turkic, such as the preservation of long vowels. Even with significant divergent features, Sakha (i.e. Yakut) is typically grouped with the Common Turkic branch of the family rather than the Oghuric branch with Chuvash. A relatively few scholars (W. Radlov and others) have expressed the view that Sakha (i.e. Yakut) is not Turkic.

Yakut is spoken mainly in the Sakha Republic. It is also used by ethnic Yakuts in Khabarovsk Region and a small diaspora in other parts of the Russian Federation, Kazakhstan, Turkey and other parts of the world. Dolgan, a close relative of Yakut, which formerly was considered by some a dialect of Yakut, is spoken by Dolgans in Krasnoyarsk Region. Yakut is widely used as a lingua franca by other ethnic minorities in the Sakha Republic – more Dolgans, Evenks, Evens and Yukagirs speak Yakut rather than their own languages. About 8% of people of ethnicities other than Yakut living in Sakha claimed knowledge of the Yakut language in the 2002 census.

Yakut has the following consonants phonemes, where the IPA value is provided in slashes '//' and the native script value is provided in bold followed by the romanization in parentheses.

Yakut is in many ways phonologically unique among the Turkic languages. Yakut and the closely related Dolgan language are the only Turkic languages without postalveolar sibilants. Additionally, no known Turkic languages other than Yakut and Khorasani Turkic have the palatal nasal /ɲ/.

Consonants at morpheme boundaries undergo extensive assimilation, both progressive and regressive. All suffixes possess numerous allomorphs. For suffixes which begin with a consonant, the surface form of the consonant is conditioned on the stem-final segment. There are four such archiphonemic consonants: G, B, T, and L. Examples of each are provided in the following table for the suffixes -GIt (second-person plural possessive suffix, oɣoɣut 'your [pl.] child'), -BIt (first-person plural possessive suffix, oɣobut, 'our child'), -TA (partitive case suffix, tiiste 'some teeth'), -LArA (third-person plural possessive suffix, oɣoloro 'their child'). Note that the alternation in the vowels is governed by vowel harmony (see the main article and the below section).