Eyak is an extinct Na-Dené language, historically spoken by the Eyak people, indigenous to south-central Alaska, near the mouth of the Copper River. The name Eyak comes from a Chugach Sugpiaq name (Igya'aq) for an Eyak village at the mouth of the Eyak River.

The closest relatives of Eyak are the Athabaskan languages. The Eyak–Athabaskan group forms a basic division of the Na-Dené language family, the other being Tlingit.

Numerous Tlingit place names along the Gulf Coast are derived from names in Eyak; they have obscure or even nonsensical meanings in Tlingit, but oral tradition has maintained many Eyak etymologies. The existence of Eyak-derived Tlingit names along most of the coast towards southeast Alaska is strong evidence that the prehistoric range of Eyak was once far greater than it was at the time of European contact. This confirms both Tlingit and Eyak oral histories of migration throughout the region.

The last surviving native speaker was Marie Smith Jones (May 14, 1918 – January 21, 2008) of Cordova.

The spread of English and suppression of aboriginal languages are not the only reasons for the decline of the Eyak language. The northward migration of the Tlingit people around Yakutat in precontact times encouraged the use of Tlingit rather than Eyak along much of the Pacific Coast of Alaska. Eyak was also under pressure from its neighbors to the west, the Alutiiq people of Prince William Sound, as well as some pressure from the people of the Copper River valley. Eyak and Tlingit culture began to merge along the Gulf Coast, and a number of Eyak-speaking groups were absorbed by the Gulf Coast Tlingit populations. This resulted in the replacement of Eyak by Tlingit among most of the mixed groups after a few generations, as reported in Tlingit oral histories of the area.

In June 2010, the Anchorage Daily News published an article about Guillaume Leduey, a French college student with an unexpected connection to the Eyak language. Beginning at age 12, he had taught himself Eyak, utilizing print and audio instructional materials he obtained from the Alaska Native Language Center. During that time, he never traveled to Alaska or conversed with Marie Smith Jones, the last native speaker.

The month that the article was published, he traveled to Alaska and met with Dr. Michael Krauss, a noted linguist and Professor Emeritus at the University of Alaska Fairbanks. Dr. Krauss assisted Leduey with proper Eyak phonological pronunciation and assigned further instruction in grammar and morphology—including morphemic analyses of traditional Eyak stories.

In June 2011, Leduey returned to Alaska to facilitate Eyak language workshops in Anchorage and Cordova. He is now regarded as a fluent speaker, translator, and instructor of Eyak. Despite his fluency, Eyak remains classified as "dormant" as there are no native speakers. On the Expanded Graded Intergenerational Disruption Scale (EGIDS) Eyak is graded a 9 (dormant); the language serves as a reminder of heritage identity for an ethnic community, but no one has more than symbolic proficiency. Currently, Leduey provides instruction and curriculum assistance to the Eyak Language Project from France.