Doclea or Duklja (Serbian Cyrillic: Дукља) was a medieval state with hereditary lands roughly encompassing the territories of present-day southeastern Montenegro, from Kotor on the west to the river Bojana on the east and to the sources of Zeta and Morača rivers on the north. Duklja was at first a vassal of the Eastern Roman Empire until it became a part of the Serbian Principality (Rascia) in the 9th century, under the Vlastimirović Dynasty. After the Byzantine annexation of Rascia in the late 10th century, Duklja was briefly under Byzantine rule but managed to liberate itself and emerged as the most powerful province in region throughout the 11th century, ruled by the Vojislavljević Dynasty.

In 1060 the Vojislavljević liberated Rascia, and when Constantine Bodin died in 1101, Rascia once again became the seat of the realm, the two principalities existing side-by-side (the period is characterized by constant changing of allegiance) until 1148 when Duklja was reinstated as a crown land of the Grand Principality of Serbia (Rascia) and is subsequently referred to as Zeta, remaining so until the fall of the Serbian Empire, when it became semi-independent in 1362 as the Lordship of Zeta, under the House of Balšić.