The Xiongnu (, xiong1.nu2) were a tribal confederation of nomadic peoples who, according to ancient Chinese sources, inhabited the eastern Eurasian Steppe from the 3rd century BC to the late 1st century AD. Modu Chanyu, the supreme leader after 209 BC, founded the Xiongnu Empire.
After overthrowing their previous overlords, the Yuezhi, the Xiongnu became the dominant power on the steppes of East Asia, centred on the Mongolian Plateau. The Xiongnu were also active in areas now part of Siberia, Inner Mongolia, Gansu and Xinjiang. Their relations with adjacent Chinese dynasties to the south-east were complex—alternating between various periods of peace, war, and subjugation. Ultimately, the Xiongnu were defeated by the Han dynasty in a centuries-long conflict, which led to the confederation splitting in two, and forcible resettlement of large numbers of Xiongnu within Han borders. During the Sixteen Kingdoms era, as one of the "Five Barbarians", they founded several dynastic states in northern China, such as the Former Zhao and Hu Xia.
Attempts to associate the Xiongnu with the nearby Sakas and Sarmatians were once controversial; however, archaeogenetics has confirmed their interaction with the Xiongnu, and also their relation to the Huns. The identity of the ethnic core of Xiongnu has been a subject of varied hypotheses, because only a few words, mainly titles and personal names, were preserved in the Chinese sources. The name Xiongnu may be cognate with that of the Huns and/or the Huna, although this is disputed. Other linguistic links—all of them also controversial—proposed by scholars include Turkic, Iranian, Mongolic, Uralic, Yeniseian, or multi-ethnic.
The Chinese name for the Xiongnu is a pejorative term in itself, as the characters (匈奴) have the meaning of "fierce slave". The pronunciation of 匈奴 as Xiōngnú xiong1nu2 is the modern Mandarin Chinese pronunciation, from the Mandarin dialect spoken now in Beijing, which came into existence less than 1,000 years ago. The Old Chinese pronunciation has been reconstructed as *xiuoŋ-na or *qhoŋna.