The Principality of Montenegro (Serbian: Књажевина Црнa Горa/Knjaževina Crna Gora) was a former realm in Southeastern Europe that existed from 13 March 1852 to 28 August 1910. It was then proclaimed a kingdom by Nikola I, who then became king.

The capital was Cetinje and the Montenegrin perper was used as state currency from 1906. The territory corresponded to the central area of modern Montenegro. It was a constitutional monarchy, but de facto absolutist.

In Danilo I's Code, dated to 1855, he explicitly states that he is the "knjaz (duke, prince) and gospodar (lord) of the Free Black Mountain (Montenegro) and the Hills" (Crna Gora and Brda). In 1870, Nikola had the title of "knjaz of Crna Gora and Brda" (књаз Црне Горе и Брда), while two years later, the state was called "knjaževina of Crna Gora" (Књажевина Црна Гора).

The Principality was formed on 13 March 1852 by Danilo I Petrović-Njegoš, when the latter, formerly known as Vladika Danilo II, decided to renounce to his ecclesiastical position as prince-bishop and married. With the first Montenegrin constitution being proclaimed in 1855, known as "Danilo's Code". After centuries of theocratic rule, this turned Montenegro into a secular principality.

Grand Duke Mirko Petrović, elder brother of Danilo I, led a strong army of 7,500 and won a crucial battle against the Turks (army of between 7,000 and 13,000) at Grahovac on 1 May 1858. The Turkish forces were routed. This victory forced the Great Powers to officially demarcate the borders between Montenegro and Ottoman Turkey, de facto recognizing Montenegro's centuries-long independence. Montenegro gained Grahovo, Rudine, Nikšić, more than half of Drobnjaci, Tušina, Uskoci, Lipovo, Upper Vasojevići, and part of Kuči and Dodoši. The glory of the Montenegrins was soon immortalized in songs and literature of all South Slavs.

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