The Despotate or Principality of Epirus (Greek: Δεσποτάτο της Ηπείρου) was one of the Byzantine Greek successor states of the Byzantine Empire that emerged in the aftermath of the Fourth Crusade in 1204. It claimed to be the legitimate successor of the Byzantine Empire, along with the Empire of Nicaea, and the Empire of Trebizond. Conquered by the Serbian Kingdom in 1337, it was restored in 1356 and existed until the Ottoman conquest in 1479.

Although the Epirote state is usually termed the "Despotate of Epirus" and its rulers called Despots, this use is not strictly accurate. The title "despot" was not even borne by all Epirote rulers. The state's founder, Michael I, never used it, and is only anachronistically referred to as "Despot of Epirus" in 14th-century Western sources. His successor Theodore did not use it either, and actually crowned himself Byzantine emperor at Thessalonica in ca. 1225. The first ruler of Epirus to receive the title of Despot was Michael II in the 1230s (from Manuel of Thessalonica), and then again, as a sign of submission and vassalage, from the Nicaean emperor John III Vatatzes. Even after that however, speaking of the Epirote rulers as "Despots of Epirus" is technically incorrect, since the title of Despot did not imply any specific territorial jurisdiction; it was merely the highest rank in the Byzantine court hierarchy, borne by close relatives to the reigning emperor, usually his sons. As a consequence, it was often borne by the princes sent to govern semi-autonomous appanages, and came to be associated later with these territories (aside from Epirus, the Despotate of the Morea is the most notable case). The term "Despotate" itself (in Greek despotaton) is not used in contemporary sources for Epirus until 1342.

Epirus /ɨˈpaɪərəs/ is a geographical and historical region in southeastern Europe, shared between Greece and Albania. It lies between the Pindus Mountains and the Ionian Sea, stretching from the Bay of Vlorë in the north to the Ambracian Gulf in the south. It is currently divided between the region of Epirus in northwestern Greece and the counties of Gjirokastër, Vlorë, and Berat in southern Albania. The largest city in Epirus is Ioannina, seat of the region of Epirus, with Gjirokastër the largest city in the Albanian part of Epirus.

A rugged and mountainous region, Epirus lay on the periphery of the ancient Greek world. It was inhabited by the Greek tribes of the Chaonians, Molossians, and Thesprotians, and home to the sanctuary of Dodona, the oldest ancient Greek oracle, and the most prestigious one after Delphi. Unified into a single state in 370 BC by the Aeacidae dynasty, Epirus achieved fame during the reign of Pyrrhus I of Epirus, whose campaigns against Rome are the origin of the term "Pyrrhic victory". Epirus subsequently became part of the Roman Empire along with the rest of Greece in 146 BC, which was followed by the Byzantine Empire. Following the fall of Constantinople to the Fourth Crusade, Epirus became the center of the Despotate of Epirus, one of the successor states to the Byzantine Empire. Conquered by the Ottoman Empire in the 15th century, Epirus became semi-independent during the rule of Ali Pasha in the early 19th century, but the Ottomans re-asserted their control in 1821. Following the Balkan Wars and World War I, southern Epirus became part of Greece, while northern Epirus became part of the newly created state of Albania.