Tolowa (; also called Chetco-Tolowa, or Siletz Dee-niü) is a member of the Pacific Coast subgroup of the Athabaskan language family. Together with three other closely related languages (Lower Rogue River Athabaskan, Upper Rogue River Athabaskan or Galice-Applegate and Upper Umpqua or Etnemitane) it forms a distinctive Oregon Athabaskan cluster within the subgroup.
At the time of first European contact Tolowa was spoken in several large and prosperous village communities along the Del Norte County coast in the far northwestern corner of California and along the southern coast of adjacent Curry County, Oregon. Today the term Tolowa (or sometimes Smith River) is used primarily by those residing in California, most of whom are affiliated with the Tolowa Dee-niü Nation. Those residing in Oregon, most of whom are affiliated with the Confederated Tribes of Siletz southwest of Portland, where their ancestors were removed in the 1850s (Beckham 1971), refer to themselves as Chetco, Tututni, or Deeniü.
For details of the linguistic documentation of Chetco-Tolowa and a survey of Oregon Athabaskan phonology and grammar, see Golla (2011:70-75).
Loren Bommelyn, a fluent speaker and linguist, has published several pedagogical books and teaches young Tolowa students in Crescent City, California.
Siletz Dee-niü is a form of Tolowa historically spoken by members of the Confederated Tribes of Siletz Indians on the Siletz Indian Reservation in Oregon, "restricted to a small area on the central Oregon coast". According to a report by the National Geographic Society and the Living Tongues Institute for Endangered Languages, it is the last of many languages spoken on the reservation and was said in 2007 to have only one living speaker. However, the language has since been at least partially revived, and in some areas, "many now text each other in Siletz Dee-ni".
Courses for 6th- through 8th-graders have been offered at Oregon's Siletz Valley Charter School. Alfred "Bud" Lane has gathered 14,000 words of Siletz Dee-niü, in an online audio/picture dictionary for the use of the community.
As with many Athabaskan languages, Tolowa features contrasting aspirated, unaspirated, and ejective stops, as well as contrasting vowel length and nasality. Tolowa is not fully tonal, but instead has a pitch accent. This is typical of the Pacific Coast Athabaskan languages.
is affricated to after vowels. is realized as after nasal vowels.
Tolowa vowels have some degree of allophonicity. and are in free variation; is an allophone of after palatals and velars; is raised to near palatals and to before velars, and is nasalized () before nasal consonants. In addition, Tolowa has three diphthongs: , , and .
Three alphabets have been used since the formation of the Tolowa Dee-niü Language program, sponsored by the Del Norte Indian Welfare Association in 1969. The first was a Tolowa version of the Uni-fon alphabet. This was created by Tom Parsons at Humboldt State University; however, after he left the university, publication in the alphabet ceased.
A new Practical Alphabet was devised in 1993 for purposes of typing on the computer.
In 1997, Loren Bommelyn developed an alphabet which replaces the nasal hook with a tilde, both è and àwith v, losing that unnecessary distinction, and à  with lh.
Syllables are usually separated with an en dash (-) for clarity.