The Mountainous Republic of the Northern Caucasus (MRNC; also known as the United Republics of the North Caucasus, Mountain Republic or the Republic of the Mountaineers) was a country in the North Caucasus formed by the unification of Circassians, Chechens, Ingush, Ossetians and Dagestanis proclaimed at the congress of the North Caucasian peoples on 6 March 1917. It existed from 1917 until 1922.

MRNC included most of the territory of the former Terek Oblast and Dagestan Oblast of the Russian Empire, which now form the republics of Chechnya, Ingushetia, North Ossetia–Alania, Kabardino-Balkaria, Dagestan, Abkhazia and part of Stavropol Krai of the Russian Federation. The total land area was about 428,264 square kilometers (165,354 sq mi), with a population of about 11 million. Its capital was initially at Vladikavkaz, then Nazran, and finally Temir-Khan-Shura.

It broke away from the Russian Empire during the February Revolution, shortly before the start of the Russian Civil War. The state was captured by Soviet Russian forces in 1921, who transformed it into the Mountain Autonomous Soviet Socialist Republic.