Tumen or tümen ("unit of ten thousand"; Mongolian Түмэн, Tümen) was a part of the decimal system used by Turkic and Mongol peoples to organize their armies. Tumen is an army unit of 10,000 soldiers. Tumen was incorporated into the Mongolian language from the Uyghur language and is also used in the Mongolian language as another word for "very many".

A mongolok jó hasznát vették a magasan képzett karakitaj hivatalnokoknak, a kitaj-ujgur kultúrának. Megbecsülték ezt a két meghódított népet.