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.

[2] 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).

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.

In the historical phonology there is a widespread tendency, observable across many Athabaskan languages, for phonemic tonal distinctions to arise from glottal features originally found at the end of the syllable.

Key evidence by current comparative methodologies includes homologies in verb prefixes and also a systematic correspondence between the distribution of Ket tones and consonant articulations found in Athabaskan–Eyak–Tlingit.

Vajda's paper has been favorably reviewed by several experts on Na-Dene and Yeniseic languages, including Michael Krauss, Jeff Leer, James Kari, and Heinrich Werner, as well as a number of other well-known linguists, including Bernard Comrie, Johanna Nichols, Victor Golla, Michael Fortescue, and Eric Hamp.

In 1925, a supporting article summarizing his thoughts, albeit not written by him, entitled "The Similarities of Chinese and Indian Languages", was published in Science Supplements.

The Sino-Dene hypothesis never gained foothold in the United States outside of Sapir’s circle, though it was later revitalized by Robert Shafer (1952, 1957, 1969) and Morris Swadesh (1952, 1965).

[8] A 2023 analysis by David Bradley using the standard techniques of comparative linguistics supports a distant genetic link between the Sino-Tibetan, Na-Dené, and Yeniseian language families.

Contemporary supporters of Greenberg's theory, such as Merritt Ruhlen, have suggested that the Na-Dené language family represents a distinct migration of people from Asia into the New World that occurred six to eight thousand years ago, placing it around four thousand years later than the previous migration into the Americas by Amerind speakers; this remains an unproven hypothesis.

[10] Ruhlen speculates that the Na-Dené speakers may have arrived in boats, initially settling near the Haida Gwaii, now in British Columbia, Canada.

[25] A large southward migration of Athabaskan peoples is thought to have occurred around 1,000 years ago, resulting in the settlement of southern North America.