Wailaki, also known as Eel River, is an extinct and revitalizing Athabaskan language spoken by the people of the Round Valley Reservation of northern California, one of four languages belonging to the California Athabaskan cluster of the Pacific Coast Athabaskan languages.

Dialect clusters reflect the four Wailaki-speaking peoples, the Sinkyone, Wailaki, Nongatl, and Lassik, of the Eel River confederation.

While less documented than Hupa, it is considered to be close to it.

It went dormant in the 1960s, but in modern times it is being revived.

Wailaki is polysynthetic, meaning that a single word in it is expressed in English as a sentence.