Yahgan or Yagán (also spelled Yaghan, Jagan, Iakan, and also known as Yámana, Háusi Kúta, or Yágankuta) is an extinct language that is one of the indigenous languages of Tierra del Fuego, spoken by the Yahgan people. It is regarded as a language isolate, although some linguists have attempted to relate it to Kawésqar and Chono.

Yahgan was also spoken briefly on Keppel Island in the Falkland Islands at a missionary settlement. In 2017, Chile's National Corporation of Indigenous Development convened a workshop to plan an educational curriculum in the Yahgan language, and in June 2019 it planned to inaugurate a language nest in the community of Bahía Mejillones, near Puerto Williams. The government also funded the publication of a "concise and illustrated dictionary" of the Yahgan language.

Following the death of Cristina Calderón (1928–2022) of Villa Ukika on Navarino Island, Chile, no native speakers of Yahgan remain.

There are three analyses of the phonological system of Yahgan, which differ in many details from one another. The oldest analysis is Thomas Bridges' dictionary (1894) based on the English Phonotypic Alphabet; from the middle of the 20th century by Haudricourt (1952) and Holmer (1953); and towards the end of the 20th century, by Guerra Eissmann (1990), Salas y Valencia (1990), and Aguilera (2000).

All vowels are long in stressed syllables. Vowel /a/ is the most frequent. It may be pronounced as a schwa [ə] in syllables in pretonic or post-tonic position. In final tonic syllables, vowels /i/ and /u/ may become a diphthong. Vowels /i/ and /o/ are very unstable in final unaccented syllables, alternating with /e/ and /u/ respectively.

Yahgan shows a number of sandhi effects on consonants and vowels. For instance, the terminal -i of teki 'to see, recognize' when affixed by -vnnaka 'to have trouble/difficulty doing' becomes -e:- of teke:vnnaka 'have trouble recognizing/seeing'

In syllables reduced through morphophonetic processes, terminal vowels (-a, -u:) of original bisyllables will often drop (except for -i, which tends to remain, leaving previous material unaffected), and resultant final stops will fricativize (r becomes sh). Aside from losing stress, any vowels preceding these shifted consonants will often shift from tense to lax. Ex. -a:gu: 'for self, with one's own' > -ax-. ata 'to take, convey' > vhr-, and so on. Present tense usually results in the dropping of the final vowel of the infinitival form of the verb and associated changes as above, as does affixation by many, but not all, further derivational and inflectional suffixes beginning with stops, affricates, and other consonants. Ex. aiamaka 'to fight' aiamux-tvlli 'to fight confusedly'.

The sounds m, n, and l are particularly labile in some environments. atama 'to eat' atu:-yella 'to leave off eating' (not atamayella). n from -Vna 'state' is often reduced to -V: when one would expect -Vn-. lt can disappear entirely before some consonants. vla 'to drink', vlnggu: or vnggu: 'to drink'. Initial h- in roots and affixes drops in many instances. Ex. kvna 'to float, be in boat'+ haina 'to walk, go' gives kvn-aina. ng (as in English 'hang') is purely morphophonetic, from terminal n before a velar consonant. Many instances of m before a labial consonant are similarly motivated. w after a passive/reflexive prefix m- often drops. w often vocalizes to u: or o: or drops (depending on preceding material): tu:- causative plus wvshta:gu: 'work' is tu:vshta:gu: 'make work'. y is also relatively labile- after reduced -ata- > -vhr- the suffix -yella 'to leave off' becomes -chella. In combination with preceding -a y often vocalizes: ki:pa 'woman' plus yamalim 'plural animates/people' becomes ki:paiamalim.