The Merkits, Chinese transcription Mie'rqi 蔑兒乞, 密兒紀, Mieliqi 蔑裡乞, Mieliji 滅裡吉, Meiliji 梅裡急 or 梅裡吉, Mo'erji 默而吉, Mai'erji 邁而吉 or Mailiji 邁禮吉, were a nomad people living in the region of River Selenga modern Mongolia during the Liao 遼 (907-1125) and Jin 金 (1115-1234) periods. Their neighbours were called Selin 森林. They lived of cattle breeding, but also of hunting and, in some places, also of agriculture. They were adherents of Nestorianism, a type of Christian faith common in Central Asia. The Merkits were divided into the tribes Wuduyi 兀都夷, Maigudan 麥古丹, Tuotuolin 脫脫鄰, Wuhuasi 兀花思 (also written Wuwasi 兀窪思) and Chahun 察渾 and were vassals to the Khitans 契丹 who had founded the Liao empire.
In 1122, when the Liao empire was crushed with the invasion of the Jurchens 女真, eventual founders of the Jin empire, part of the Merkit joined the Khitan prince Yelü Dashi 耶律大石 who migrated to the west, where he founded the Western Liao empire 西遼 (1124-1218). The Merkits were known as a very belligerent people that often engaged in conflicts with other Mongol tribes.
The Secret History of the Mongols narrates how the Mongol chieftain Yesügai Baatur 也速該把阿禿爾 robbed a freshly married bride from the Merkits, who became the mother of Temüjin 鐵木真, the eventual Chinggis Khan 成吉思汗. From then on the two peoples constantly fought against each other. The Merkits also had often conflicts with their western neighbours, the Kereyids 克烈. The Merkit chieftain Toghto 脫脫 later attacked Temüjin and kidnapped his family. Temüjin joined with the Kereyid leader Wanghan 王罕 and Jamuhe 劄木合, leader of the Jalayirs 茶札剌, and forced the Merkits into battle at River Buwula 不兀剌.
In 1201 the Merkits joined with the Jalayirs and attacked Temüjin, but the allies were heavily defeated. In 1204, shortly after Temüjin's victory over the Naimans 乃蠻 under Taiyang Khan 太陽罕, Temüjin attacked the Merkits and forced the tribes of the Maigudan, Tuotuoli and Chahun to submit. Toghto fled to Buyulu Khan 不欲魯 of the Naimans. Two years later Buyulu Khan was defeated by the Mongols, and Toghto, and Taiyang Khan's son Quchulü 屈出律 fled to the region of the rivers Yerdish and Buheidurma (today River Irtysh), where he was killed shortly later. The rest of the Merkits were forced to join the Mongol federation.