quality:corruption, structural:reformatting
Yeniseian theories

Lajos Ligeti was the first to suggest that the Xiongnu spoke a Yeniseian language. In the early 1960s Edwin Pulleyblank was the first to expand upon this idea with credible evidence. The Yeniseian theory proposes that the Jie, a western Xiongnu people, spoke a Yeniseian language. Hyun Jin Kim notes that the 7th AD Chinese conpendium, Jin Shu, contains a transliterated song of Jie origin, which appears to be Yeniseian. This song has led researchers Pulleyblank and Vovin to argue for a Yeniseian Jie dominant minority, that ruled over the other Xiongnu ethnicities, like Iranian and Turkic people. Kim has stated that the dominant Xiongnu language was likely Turkic or Yeniseian, but has cautioned that the Xiongnu were definitely a multi-ethnic society.

Pulleybank and D. N. Keightley asserted that the Xiongnu titles "were originally Siberian words but were later borrowed by the Turkic and Mongolic peoples". Titles such as tarqan, tegin and kaghan were also inherited from the Xiongnu language and are possibly of Yeniseian origin. For example, the Xiongnu word for "heaven" is theorized to come from Proto-Yeniseian * tɨŋVr.

Vocabulary from Xiongnu inscriptions sometimes appears to have Yeniseian cognates which were used by Vovin to support his theory that the Xiongnu has a large Yeniseian component, examples of proposed cognates include words such as Xiongnu kʷala 'son' and Ket qalek 'younger son', Xiongnu sakdak 'boot' and Ket sagdi 'boot', Xiongnu gʷawa "prince" and Ket gij "prince", Xiongnu "attij" 'wife' and proto-Yeniseian "alrit", Ket "alit" and Xiongnu dar "north" compared to Yugh tɨr "north". Pulleyblank also argued that because Xiongnu words appear to have clusters with r and l, in the beginning of the word it is unlikely to be of Turkic origin, and instead believed that most vocabulary we have mostly resemble Yeniseian languages.

Alexander Vovin also wrote, that some names of horses in the Xiongnu language appear to be Turkic words with Yeniseian prefixes.

An analysis by Savelyev and Jeong (2020) has cast doubt on the Yeniseian theory. If assuming that the ancient Yeniseians were represented by modern Ket people, who are more genetically similar to Samoyedic speakers, the Xiongnu do not display a genetic affinity for Yeniseian peoples. A review by Wilson (2023) argues that the presence of Yeniseian-speakers among the multi-ethnic Xiongnu should not be rejected, and that "Yeniseian-speaking peoples must have played a more prominent (than heretofore recognized) role in the history of Eurasia during the first millennium of the Common Era".