Oirats (Mongolian: Ойрад, Oirad; in the past, also Eleuths) are the westernmost group of the Mongols who unified several tribes origin whose ancestral home is in the Altai region of western Mongolia. Although the Oirats originated in the eastern parts of Central Asia, the most prominent group today is located in the Republic of Kalmykia, a federal subject of the Russian Federation, where they are called Kalmyks. The Kalmyks migrated from Dzungaria to the southeastern European part of the Russian Federation in the early XVII century.

Historically, the Oirats were composed of four major tribes: Dzungar (Choros or Ööled), Torghut, Dörbet, and Khoshut. The minor tribes include: Khoid, Bayid, Myangad, Zakhchin, Baatud, Barga and Darkhad.

In the 17th century, Zaya Pandita, a Gelug monk of the Khoshut tribe, devised a new writing system called Todo Bichig (clear script) for use by the Oirat people. This system was developed on the basis of the older Mongolian script, but had a more developed system of diacritics to exclude misreading, and reflected some lexic and grammar differences of the Oirat language from Mongolian.