Klamath (/ˈklæməθ/), also Klamath–Modoc (/ˈklæməθ ˈmoʊdɒk/) and historically Lutuamian (/ˌluːtuˈæmiən/), is a Plateau Penutian language spoken around Klamath Lake in what is now southern Oregon and northern California. It is the traditional language of the Klamath and Modoc peoples, each of whom spoke a dialect of the language. By 1998, only one native speaker remained, and by 2003, this last fluent Klamath speaker who was living in Chiloquin, Oregon, was 92 years old. As of 2006 there were no fluent native speakers of either the Klamath or Modoc dialects; however, as of 2019, revitalization efforts are underway with the goal of creating new speakers.
Klamath is a member of the Plateau Penutian language family, which is in turn a branch of the proposed Penutian language family. Like other proposed Penutian languages, Plateau Penutian languages are rich in ablaut, much like Indo-European and Afro-Asiatic languages. Further evidence for this classification includes some consonant correspondences between Klamath and other alleged Penutian languages. For example, the Proto-Yokuts retroflexes */ʈ ʈʼ/ correspond to Klamath /tʃ tʃʼ/, and the Proto-Yokuts dentals */t̪ t̪ʰ t̪ʼ/ correspond to the Klamath alveolars /t tʰ tʼ/.