Armenia and Azerbaijan share a complicated and conflict-prone ethnic, religious and geopolitical history, and their international boundary remains undelimited and de facto. Furthermore, the two States share multiple frontiers: a primary international boundary between Armenia and Azerbaijan proper, the boundary between the Azerbaijani exclave of Nakhchivan with southwestern Armenia, and the Armenian-backed separatist territory of Nagorno-Karabakh, also known as the Republic of Artsakh, which is completely enclaved by Azerbaijan. 

The focus of this report is on the main international boundary between Armenia and Azerbaijan proper, running in a north to south direction, mostly along watersheds, between de facto tripoints with Georgia in the north and Iran in the south. This undelimited and de facto boundary extends for approximately 870 kilometers (540 miles) and contains many areas of dispute and contention.

The de facto international boundary stems from internal administrative lines established while both countries were under Russian control in the 19th and 20th centuries, both as part of the Tsarist Empire and later the Union of Soviet Socialist Republics. Since independence in 1991, Armenia and Azerbaijan have fought multiple wars, and the precise location of the boundary remains undefined.

In the fall of 2020, Armenia and Azerbaijan entered into a three-month conflict over the separatist territory of the Republic of Artsakh. Following a November 2020 ceasefire Agreement, the two States have been encouraged to delimit and demarcate the primary international boundary. While negotiations have begun, little progress towards a complete boundary delimitation has been made.