Shiwei (simplified Chinese: 室韦; traditional Chinese: 室韋; pinyin: Shìwéi; Wade–Giles: Shih⁴-wei²) were a Mongolic people that inhabited far-eastern Mongolia, northern Inner Mongolia, northern Manchuria and the area near the Okhotsk Sea beach. Records mentioning the Shiwei were recorded from the time of the Northern Wei (386–534) until the rise of the Mongols under Genghis Khan in 1206 when the name "Mongol" and "Tatar" were applied to all the Shiwei tribes.

The Shiwei-Mongols were closely related to the Khitan people to their south. As a result of pressure from the west, south and south-east they never established unified, semi-sedentarized empires like their neighbors, but remained nomadic confederations led by tribal chieftains, alternately submitting to the Turks, the Chinese and the Khitan as the political climate changed. The Mengwu Shiwei, one of the 20 Shiwei tribes during the Tang dynasty (618–907), were also called the Menggu during the Liao dynasty (907–1125) and are generally considered to be the ancestors of the Mongols of Genghis Khan. The modern Korean pronunciation of Mengwu (蒙兀 Měngwù) is Mong-ol (/moŋ.ol/). Mongolia is still called "Menggu" (蒙古 Měnggǔ) in Chinese today.

The names Shiwei, Sibe, Xibe and possibly Xianbei have a common origin.

The Shiwei were descendants of the Yuwen Xianbei, but also included some tribes of the Tungusic Mohe people. Shiwei is a variant transcription for Xianbei.

Chinese dynastic histories describe the Shiwei as somewhat related to the Khitan, who were of Xianbei origin. They were local Xianbei tribes who became independent after the Xianbei state dissolved in 234 with the death of Budugen. In the Book of Wei, it is claimed that the language of the Shiwei was the same as the Khitan's, who spoke the Khitan language; in the Book of Sui, it is claimed that the Shiwei belonged to the same kind of people as the Khitan; and in both the New Book of Tang and Old Book of Tang, it is claimed that the Shiwei were a collateral branch of the Khitan. It is likely that at least some tribes of the Shiwei had some ethnic similarities with the Khitan. Tang dynasty historian Wan Guowei describes the Shiwei as a Khitan tribe.

The Book of Sui states that the title of the northern Shiwei chieftain was Mohefu, which is the same as the Khitan title for their chieftain – Mohefu (traditional Chinese: 莫賀弗) or "Mofuhe" (traditional Chinese: 莫弗賀), which is the Chinese transliteration of the Iranic/Sogdian title Bagapuhr/βɣpwr, meaning "Son of God". For example, the Khitan Mofuhe Hechen who paid tribute to the Northern Wei at Datong in 466–470 and the Khitan Mofuhe Wuyu who fled from Goguryeo and the Rouran Khaganate in 479.

Concerning the ethnic relationship between the Shiwei and the Khitan, "the ethnonymic distinction between the Shiwei and Khitan suggests that the division had been completed between the branches leading to Proto-Mongolic and Para-Mongolic".

The Shiwei and Wuluohou are known as the Shiwei tribes in the period of the Northern Wei dynasty (386–534), but are separately recorded in the Book of Wei. During the period from the Northern Qi (550–577) to the Sui dynasty (581–618), there were five groups of Shiwei, they were the Nan (Southern) Shiwei, Bei (Northern) Shiwei, Da (Great) Shiwei, Bo Shiwei and Shenmoda Shiwei. In the Tang period (618–907), it is known that there were twenty Shiwei tribes, according to the records in dynastic histories. They were the Wusugu, Yisaimo, Saiezhi, Hejie, Wuluohu, Nali, Lingxi, Shanbei, Huangtou (Yellow-head), Da (Great) Ruzhe, Xiao (Lesser) Ruzhe, Powo, Nebeizhi, Luotuo, Dong (Eastern) Shiwei, Xi (Western) Shiwei, Da (Great) Shiwei, Mengwu Shiwei, Luozu Shiwei and Dagui.