The Montenegrin People's Socialist Republic (MNPSR; Montenegrin: Црногорска Народна Социјалистичка Република, ЦГНСР Tsrnogorska Narodna Sotsijalistička Republika, TsNSR), informally known as Montenegro (Црна Гора Tsrna Gora; lit. "Black Mountain"), is a socialist republic located in the Balkans region of Southern Europe on the eastern coast of the Adriatic Sea. It is one of seven constituent republics of Yugoslavia, and borders the Bosnian-Herzegovinian People's Socialist Republic to the northwest, the Serbian People's Socialist Republic to the northeast, the Kosovar People's Autonomous Socialist Republic to the east, all of which are fellow republics of Yugoslavia, and the sovereign state of Albania to the south.
Montenegro is officially a unitary, secular, socialist republic; it is governed by the Communist Party of Montenegro, with its capital in Podgorica, Montenegro's largest city, which is one of the republic's 23 municipalities. Its official language is Montenegrin, a standardised register of the wider Serbo-Croatian language.
During the Medieval period, three principalities were located on the territory of modern-day Montenegro: Duklja, roughly corresponding to the southern half; Travunia, the west; and Rascia, the north. In 1042, archon Stefan Vojislav led a revolt that resulted in the independence of Duklja from the Byzantine Empire and the establishment of the Vojislavljević dynasty. The independent Principality of Zeta emerged in the 14th and 15th centuries, ruled by the House of Balšić between 1356 and 1421, and by the House of Crnojević between 1431 and 1498, when the name Montenegro started being used for the country. After falling under Ottoman rule, Montenegro regained de facto independence in 1697 under the rule of the House of Petrović-Njegoš, first under the theocratic rule of prince-bishops, before being transformed into a secular principality in 1852. Montenegro's de jure independence was recognised by the Great Powers at the Congress of Berlin in 1878, following the Montenegrin–Ottoman War. In 1905, the country became a kingdom. After World War I, it became part of Yugoslavia.
Today, the Montenegrin Socialist Republic is a highly developed nation, with a robust economy primarily based around tourism and the service industry. With a population of just over 600,000 people, Montenegro is the least populous of the federated entities of Yugoslavia.