This article discusses the complex history of Mongolia during the Xiongnu Period (209 BCE – 2nd Century CE). The origins of the Xiongnu are still relatively unknown to archaeologists. I describe on-going research of these pastoral nomads and attempt to elucidate questions of their provenience and biological relationships to other groups in the region, specifically to groups in China and Siberia. Current hypotheses suggest a complex population history, and data from bones, genes, and artifacts attest to this complexity. Here, I show that the Xiongnu are not entirely biologically homogenous and are closely related to both nomadic Chinese and Siberian populations.