In February 2008, a proposal connecting Na-Dene (excluding Haida) to the Yeniseian languages of central Siberia into a Dené–Yeniseian family was published and well received by a number of linguists. It was proposed in a 2014 paper that the Na-Dene languages of North America and the Yeniseian languages of Siberia had a common origin in a language spoken in Beringia, between the two continents.
Edward Sapir originally constructed the term Na-Dene to refer to a combined family of Athabaskan, Tlingit, and Haida (the existence of the Eyak language was not known to him at the time). In his "The Na-Dene languages: A preliminary report", he describes how he arrived at the term (Sapir 1915, p. 558):
The name that I have chosen for the stock, Na-dene, may be justified by reference to no. 51 of the comparative vocabulary. Dene, in various dialectic forms, is a wide-spread Athabaskan term for "person, people"; the element *-ne (*-n, *-η) which forms part of it is an old stem for "person, people" which, as suffix or prefix, is frequently used in Athabaskan in that sense. It is cognate with H. na "to dwell; house" and Tl. na "people". The compound term Na-dene thus designates by means of native stems the speakers of the three languages concerned, besides continuing the use of the old term Dene for the Athabaskan branch of the stock.
In its non-controversial core, Na-Dene consists of two branches, Tlingit and Athabaskan–Eyak:
For linguists who follow Edward Sapir in connecting Haida to the above languages, the Haida isolate represents an additional branch, with Athabaskan–Eyak–Tlingit together forming the other. Dene or Dine (the Athabaskan languages) is a widely distributed group of Native languages spoken by associated peoples in Alberta, British Columbia, Manitoba, Northwest Territories, Nunavut, Saskatchewan, Yukon, Alaska, parts of Oregon, northern California, and the American Southwest as far as northern Mexico.
The southwestern division of Athabaskan is also called Southern Athabaskan or Apachean, and includes Navajo and all the Apache dialects. Eyak was spoken in south-central Alaska; the last speaker died in 2008. Navajo is by far the most widely spoken language of the Na-Dene family, spoken in Arizona, New Mexico, and other regions of the American Southwest.
All of these languages share a highly complex prefixing verb structure in which tense and mood markers are interdigitated between subject and object agreement markers. The morphological hallmark of the family is a series of prefixes found directly before the verb root that raise or lower the transitivity of the verb word. These prefixes, traditionally known as "classifiers", derive historically from a combination of three distinct classes of morphemes and are not found in any other Native American language family.