The Xueyantuo or Sir Tardush were an ancient Turkic tribe from the Tiele confederation and a khaganate in Northeast Asia who were at one point vassals of the Göktürks, later aligning with the Tang dynasty against the Eastern Turkic Khaganate.

Xue 薛 appeared earlier as Xinli 薪犁 in Sima Qian's Shiji, vol. 110 but were not referred to again until the 7th century. Golden (2011) proposed that 薛 Xue's Old Turkic form Sir derived from Sanskrit Śrī "fortunate, auspicious"

The etymology of Yantuo 延陀 is much debated. It was first identified with Tarduš, one of two divisions, besides Töliš, of the short-lived Xueyantuo Qaghanate, by Western Orientalists (like Vilhelm Thomsen) who considered Töliš and Tarduš to be tribal names. The ethnonym is thus reconstructable as Syr-Tardush. However, Chinese scholars viewed Töliš and Tarduš as names of political organizations or districts: for example, Cen Zhongmian viewed the Töliš-Tarduš division as east–west whereas Wang Jingru, citing the New Book of Tang, viewed Töliš-Tarduš as north–south.

Sergey Klyastorny (2003:305), apud Golden (2018), proposed that Xueyantuo transcribed *Sir-Yamtar; in contrast to the tribal name Sir, [Ïšβara] Yamtar appeared as a personal name of one companion of Kül Tigin, mentioned the eponymous inscription in his memory.

The Tongdian records the origin of Yantuo: "During the reign of Murong Jun in the Former Yan, the Xiongnu chanyu Helatou (賀剌頭, "the leader of the Alat tribe") led his tribe of thirty-five thousand people and came to surrender. Yantuo people are probably their descendants." Based on this, Bao (2010) proposed that Yantuo people were the descendants of the Alat tribe, also known as Hala-Yundluɣ; therefore, the name Yantuo was probably derived from Yundluɣ, and Xueyantuo can be reconstructed as Sir-Yundluɣ.

Initially the Xue and the Yantuo were two separate tribes. The Tongdian states that: "Xueyantuo is a splinter tribe from Tiele. In the time of Former Yan [emperor] Murong Jun, Xiongnu Shanyu Helatou led his tribe, numbering 35,000, to come surrender. Yantuo are probably their descendants. With the Xue tribe [Yantuo] live intermixed. Thus the appellation Xueyantuo. The Khagan clan's surname is Yilitu. For generations they have been a strong nation." The rulers of Xueyantuo claimed to be originally named Xue (薛/偰), and that the name of the tribe was changed to Xueyantuo after the Xue defeated and merged the Yantuo into their tribe.

After Yiedie Khan, the Xueyantuo founded a short-lived khaganate over the steppe under Zhenzhu Khan, his son Duomi Khan and nephew Yitewushi Khan, the last of whom eventually surrendered to the Tang dynasty.

In 605, Xueyantuo were attacked by the Western Turkic Khaganate under Heshana Qaghan. Consequently, they abandoned the Western Turks and established their own khaganate under a leadership of Qibi tribe's Yiwuzhenmohe Qaghan, retaining the control and income from the Turpan segment of the Silk Road. Later, Xueyantuo leader Yshbara was installed as a lesser kagan yetir (yeti er "seven tribes"). In 610, Shikui Khagan (r. 610–617) ascended to the Western Turkic throne, both rulers renounced their kagan ranks and rejoined the Western Turkic Khaganate. The next Western Turkic ruler, Tong Yabghu Qaghan (r. 618–628) annexed all seven tribes of the Xueyantuo-headed Tiele confederation, which also included Uyghur, Bayïrku, Ădiz, Tongra, Bugu and Barsil tribes. In 627 the Xueyantuo leader led his tribes into the territory of the Eastern Turkic Khaganate, defeated the main force of the khaganate led by the son of the reigning Illig Qaghan, Yukuk Shad, and settled in the valley of river Tola in the northern Mongolia. After the victory, Uyghur leader Yaoluoge Pusa assumed a title huo xielifa (Chinese: 活頡利發 *kat-elteber or *war-hilitber) and split from the confederation, and in 629 the Xueyantuo Yinan-erkin declared himself Inčü Bilge-Khagan of the new Xueyantuo Khaganate.