The Defense Army of the Republic of Artsakh (Armenian: Արցախի Հանրապետության պաշտպանության բանակ, romanized: Artsakhi Hanrapetut’yan pashtpanut’yan banak) was the defence force of the breakaway Republic of Artsakh. Established in 1992, it united previously disorganized defence units which were formed in the early 1990s.

It was disbanded on 20 September 2023 under the terms of the Nagorno-Karabakh ceasefire agreement following the 2023 Azerbaijani military offensive.

The Artsakh Defence Army was founded on 9 May 1992. It created "its own central command and military structure distinct from the Armenian Army." Its founders included Robert Kocharyan (the former President of Armenia, he was the first commander-in-chief of the Army); Serzh Sargsyan (former Prime Minister and President of Armenia); Vazgen Sargsyan (Armenia's Defence Minister 1992–93, State Minister in Charge of defence 1993–95, Armenia's Prime Minister 1998–99); Monte Melkonian (responsible for Martuni Province); Samvel Babayan (Nagorno-Karabakh's Defence Minister from 1994 to 2000) and others. Many of the men who served in its ranks and in the officer corps during the First Nagorno-Karabakh War were seasoned veterans of the Soviet military and had fought in the Soviet–Afghan War.

The formal formation of the NKR Defence Army was rooted in the concept of the Jokat (volunteer detachment). With the early outbreak of hostilities prior to 1992, Armenians of Nagorno-Karabakh began forming small detachments of volunteers, often self-described as Fedayeen, inheriting the name of the fighters who actively resisted the Ottoman Empire in the final decades of the nineteenth and early decades of the twentieth centuries.

At the outset these detachments were small groups of no more than 12–40 men. For example, during Operation Ring, Shahumyan was defended by a force as small as 22 men under the command of Tatul Krpeyan. These volunteer militia would initially arm themselves with whatever was available, including hunting shotguns borrowed from local farmers and even home-made rifles. In the later stages of the war, these units armed themselves with AK-47s, RPGs and sometimes MANPADs, transforming the defence force into a highly mobile and flexible force that was capable of waging guerrilla warfare. Likewise, these units initially had no heavy military equipment, but later started taking over large quantities of Azerbaijani tanks and armored personnel carriers that were abandoned on the battlefield. Most of these captured tanks and APCs later became part of the NKR Defense Army's equipment. Improvization, multi-functionality, creativity, strong-morale, focus on defensive tactics, adaptation, flexibility, high-mobility and a native knowledge of the mountainous terrain were all important factors in understanding the combat success of these small units.^{[citation needed]}

The initial purpose of these detachments, made up of volunteers, was mainly to defend Armenian civilian population, each in a particular village or town. Each of them was operating independently with no central command or leadership. Yet, these units would regularly collaborate in joint operations such as the battle of Khojaly in February 1992 or the June 1992 surprise counter-offensives during Operation Goranboy. The increasing scale and intensity of Azerbaijani attacks, the devastation caused by Grad multiple rocket launchers firing from Shusha and the Lachin, the blockade from mainland Armenia had broadened the notion of security beyond the mere defence of a small village. Capturing Shusha and Lachin as well as turning the tide of Operation Goranboy became, for the Armenians, not only a matter of security, but that of survival. For the successful conduct of such large-scale operations, the detachments had to be consolidated under a single, unified command.^{[citation needed]}

Mient Jan Faber argues that "August 1992 marked the watershed between purely voluntary Armenian Karabakh forces reinforced by volunteers from Armenia and an organised NKR army with its own central command and a military structure distinct from the Armenian army."

The Nagorno-Karabakh Defence Army's primary role after the conclusion of the First Nagorno-Karabakh War in 1994 was the protection of the NKR from foreign and domestic threats. Though the war ended with the signing of a cease fire between Armenia, Nagorno-Karabakh and Azerbaijan and the de facto independence of the NKR, the Azerbaijani leadership repeatedly threatened to restart hostilities to retake the region. Violations of the cease fire along the line of contact were frequent and often resulted in the deaths of several soldiers and civilians each year. One of the most significant breaches of the ceasefire occurred in Martakert on 8 March 2008, when up to sixteen soldiers were killed. Both sides accused the other of starting the battle. In June 2010, new skirmishes broke out between Armenian and Azerbaijani troops along the line of contact, resulting in the deaths of four Armenian servicemen. Clashes in summer 2014 resulted in the deaths of six Armenian and thirteen Azerbaijani servicemen. On 12 November 2014, a Nagorno-Karabakh Defence Army Mi-24 attack helicopter participating in the week-long joint Armenian–NKR Unity 2014 military exercises was shot down by the Azerbaijani military, killing all three crew members. On 1 April 2016 large scale clashes began along the line of contact, which lasted for four days and came to be known as the Four-Day War. According to several sources they were the worst since 1994. These clashes culminated in the 2020 Nagorno-Karabakh war, in which the Artsakh Defence Army was defeated while fighting against the military of Azerbaijan and Turkey. Turkish President Recep Tayyip Erdogan Erdogan admitted that Turkey provided military and diplomatic backing to Azerbaijan during the fighting. During the war, Turkey sent a number of Syrian opposition fighters as mercenaries to fight against Armenian forces, including fighters from Sultan Murad Division and Hamza Division.