Artsakh (/ˈɑːrtsɑːx, -sæx/ ART-sa(h)kh), officially the Republic of Artsakh or the Republic of Nagorno-Karabakh (/nəˌɡɔːrnoʊ kərəˈbɑːk/ nə-GOR-noh kər-ə-BAHK), was a breakaway state in the South Caucasus whose territory was internationally recognised as part of Azerbaijan. Between 1991 and 2023, Artsakh controlled parts of the former Nagorno-Karabakh Autonomous Oblast of the Azerbaijani Soviet Socialist Republic, including its capital Stepanakert. It had been an enclave within Azerbaijan from the 2020 Nagorno-Karabakh war until the 2023 Azerbaijani offensive, when the Azerbaijani military took control over the remaining territory controlled by Artsakh. Its only overland access route to Armenia after the 2020 war was via the five-kilometre-wide (3.1 mi) Lachin corridor, which was placed under the supervision of Russian peacekeeping forces.

The predominantly Armenian-populated region of Nagorno-Karabakh was claimed by both the Azerbaijan Democratic Republic and the First Republic of Armenia when both countries became independent in 1918 after the fall of the Russian Empire. A brief war over the region broke out in 1920. The dispute was largely shelved after the Soviet Union established control over the area, and created the Nagorno-Karabakh Autonomous Oblast (NKAO) within the Azerbaijan SSR in 1923; however, throughout the Soviet period, Armenians in the Nagorno-Karabakh Autonomous Oblast were heavily discriminated against. The Soviet Azerbaijani authorities worked to suppress Armenian culture and identity in Nagorno-Karabakh, pressured Armenians to leave the region and encouraged Azerbaijanis to settle within it, although Armenians remained the majority population.

The local Armenians of the area, motivated by fears of cultural and physical erasure under government policies from Azerbaijan, began the 1988 Karabakh movement advocating for reunification (Miatsum) with Armenia.^{[verification needed]} This was met with extreme violence from Azerbaijani authorities and civilians, escalating tensions and culminating in a referendum in 1991 which overwhelmingly opted for independence. The conflict erupted into a full-out war in 1992. The war was won by Artsakh with support from Armenia. Although a ceasefire agreement was signed in 1994, the frozen situation left the predominantly Armenian-populated territory de facto independent, with a self-proclaimed government in Stepanakert, but still heavily reliant on and closely integrated with Armenia, in many ways functioning as a de facto part of Armenia. Even though Armenia never officially recognized the region's independence, it became the main financial and military supporter of the territory. In 2017, a referendum in the area approved a new constitution that transformed the system of government from a semi-presidential to a presidential democracy with a unicameral legislature in addition to changing the name of the state from the Republic of Nagorno-Karabakh to the Republic of Artsakh, although both names remained official.

From 1994 until 2020, Armenian and Azerbaijani troops remained separated by a contested line of contact which saw sporadic deadly incidents during the intervening years. In 2020, a new war was fought in the region, with Azerbaijan achieving victory and regaining all the surrounding occupied districts and a significant portion of Artsakh's claimed territory. The Lachin corridor linking Artsakh to Armenia was blockaded by Azerbaijan in December 2022. In September 2023, Azerbaijan launched another military offensive. The government of Artsakh agreed to disarm and enter talks with Azerbaijan, prompting a flight of ethnic Armenians from the area. On 28 September 2023, the president of Artsakh signed a decree to dissolve all of the republic's institutions by 1 January 2024, though the president later attempted to annul this decree. By 1 October 2023, almost the entire population of the region had fled to Armenia, marking the end of a millennia-old Armenian presence in Nagorno-Karabakh.

According to scholars, inscriptions dating to the Urartian period mention the region under a variety of names: "Ardakh", "Urdekhe", and "Atakhuni". In his Geography, the classical historian Strabo refers to an Armenian region which he calls "Orchistene", which is believed by some to be a Greek version of the old name of Artsakh.

According to another hypothesis put forth by David M. Lang, the ancient name of Artsakh possibly derives from the name of King Artaxias I of Armenia (190–159 BC), founder of the Artaxiad dynasty and the kingdom of Greater Armenia.

Folk etymology holds that the name is derived from "Ar" (Aran) and "tsakh" (woods, garden) (i.e., the gardens of Aran Sisakean, the first nakharar of northeastern Armenia).

The name "Nagorno-Karabakh", commonly used in English, comes from the Russian name which means "Mountainous Karabakh". Karabakh is a Turkish/Persian word thought to mean "black garden". The Azerbaijani name for the area, "Dağlıq Qarabağ", has the same meaning as the Russian name. The term "Artsakh" lacks the non-Armenian influences present in "Nagorno-Karabakh". Artsakh was revived for use in the 19th century, and was the preferred term used by the population, in English and Russian as well as Armenian. "Mountainous Karabakh" was sometimes employed directly as part of the official English name, "Republic of Mountainous Karabakh". This reflected an attempt to shift away from the negative associations thought linked with "Nagorno-Karabakh" due to the war.