Gandzasar is a 13th-century Armenian Apostolic cathedral (historically a monastery) near the village of Vank in the Martakert Province of the self-proclaimed Republic of Artsakh, de jure in the Kalbajar District of Azerbaijan.

It has historically been the region's most important church since its foundation. One of the finest pieces of Armenian architecture of the mid-1200s, the building is best known among scholars for its richly decorated dome.

The name Gandzasar, which means "treasure mountain" in Armenian, is believed to have originated from the tradition that the monastery was built on a hill containing ores of silver and other metals.

The site was first mentioned in written records by the tenth century Catholicos Anania of Moks (r. 946-968), who listed Sargis, a monk from Gandzasar, among the participants of a 949 council convened in Khachen to reconcile Chalcedonian and non-Chalcedonian Armenians. Khachkars dated 1174, 1182, and 1202 have been found around the monastery, which also point to the existence of a church or monastery at the site.

The main church was built between 1216 and 1238 by Hasan-Jalal Dawla, the Armenian prince of Inner Khachen and the patriarch of the House of Hasan-Jalalyan. It was consecrated on July 22, 1240, on the Feast of the Transfiguration (Vardavar) in attendance of some 700 priests. The gavit (narthex), to the west of the church, was started in 1240 and completed in 1266 by Atabek, the son of Hasan-Jalal and his wife, Mamkan. Kirakos Gandzaketsi, a contemporary historian, described the construction of the church in his History of Armenia.