Chuvash (UK: /ˈtʃuːvɑːʃ/ CHOO-vahsh, US: /tʃʊˈvɑːʃ/ chuu-VAHSH; Чӑваш чӗлхи, Чӑвашла, translit. Çăvaşla, IPA: [tɕəʋaʃˈla]) is a Turkic language spoken in Volga-Ural region of Russia, primarily in the Chuvash Republic and adjacent areas. It is the only surviving member of the Oghur branch of Turkic languages, one of the two principal branches of the Turkic family.

The writing system for the Chuvash language is based on the Cyrillic script, employing all of the letters used in the Russian alphabet and adding four letters of its own: Ӑ, Ӗ, Ҫ and Ӳ.

Chuvash is the native language of the Chuvash people and an official language of Chuvashia. There are contradictory numbers regarding the number of people able to speak Chuvash nowadays; some sources claim it is spoken by 1,640,000 persons in Russia and another 34,000 in other countries and that 86% of ethnic Chuvash and 8% of the people of other ethnicities living in Chuvashia claimed knowledge of Chuvash language during the 2002 census. However, other sources claim that the number of Chuvash speakers is on the decline, with a drop from 1 million speakers in 2010 to 700,000 in 2021; observers suggest this is due to Moscow having a lack of interest in preserving the language diversity in Russia. Although Chuvash is taught at schools and sometimes used in the media, it is considered endangered by the UNESCO, because Russian dominates in most spheres of life and few children learning the language are likely to become active users.

A fairly significant production and publication of literature in Chuvash still continues. According to UNESCO's Index Translationum, at least 202 books translated from Chuvash were published in other languages (mostly Russian) since ca. 1979. However, as with most other languages of the former USSR, most of the translation activity took place before the dissolution of the USSR: out of the 202 translations, 170 books were published in the USSR and just 17, in the post-1991 Russia (mostly, in the 1990s). A similar situation takes place with the translation of books from other languages (mostly Russian) into Chuvash (the total of 175 titles published since ca. 1979, but just 18 of them in post-1991 Russia).

Chuvash is the most distinctive of the Turkic languages and cannot be understood by other Turkic speakers, whose languages have varying degrees of mutual intelligibility within their respective subgroups. Chuvash is classified, alongside the long-extinct Bulgar, as a member of the Oghuric branch of the Turkic language family, or equivalently, the sole surviving descendant of West Old Turkic. Since the surviving literary records for the non-Chuvash members of Oghuric (Bulgar and possibly Khazar) are scant, the exact position of Chuvash within the Oghuric family cannot be determined.

Despite grammatical similarity with the rest of Turkic language family, the presence of changes in Chuvash pronunciation (which are hard to reconcile with other members of the Turkic family) has led some scholars to see Chuvash as originating not from Proto-Turkic but from another proto-language spoken at the time of Proto-Turkic (in which case Chuvash and all the remaining Turkic languages would be part of a larger language family).

Italian historian and philologist Igor de Rachewiltz noted a significant distinction of the Chuvash language from other Turkic languages. According to him, the Chuvash language does not share certain common characteristics with Turkic languages to such a degree that some scholars consider Chuvash as an independent branch from Turkic and Mongolic. The Turkic classification of Chuvash was seen as a compromise solution for classification purposes.

The Oghuric branch is distinguished from the rest of the Turkic family (the Common Turkic languages) by two sound changes: r corresponding to Common Turkic z and l corresponding to Common Turkic š. The first scientific fieldwork description of Chuvash, by August Ahlqvist in 1856, allowed researchers to establish its proper affiliation.