The Duchy of Neopatras (Catalan: Ducat de Neopàtria; Modern Greek: Δουκάτο Νέων Πατρών; Latin: Ducatus Neopatriae) was one of the Crusader States set up in Greece after the sacking and conquest of the Byzantine Empire during the Fourth Crusade. It was situated in Central Greece, centered on the city of Neopatras (Νέαι Πάτραι, Neai Patrai), modern Ypati) in the Spercheios valley, west of Lamia.
When the Greek ruler of Thessaly, John II Doukas, died in 1318 without heir, his domains fell into anarchy. The Almogavars of the Catalan Company, who had recently conquered most of the Duchy of Athens to the south of Thessaly, took advantage of the situation to push north. The Catalans took Neopatras in 1319, and by 1325 had also conquered Zetounion, Loidoriki, Siderokastron and Vitrinitsa, as well as - apparently briefly - Domokos, Gardiki and Pharsalus. The central and northern part of Thessaly remained in Greek hands.
The Catalans selected the infant Manfred, son of King Frederick III of Sicily, as their duke, but actual power was wielded by the Duke's local representative, the vicar-general, as well as by the marshal (mariscalus exercitus ducatuum) as the elected head of the Company members.
Most of the Duchy's possessions in Thessaly were lost when the region was conquered by the Serbs of Stefan Dushan in 1348, but Neopatras and the region around it remained in Catalan hands. In 1377, the title of Duke of Athens and Neopatras was assumed by Peter IV of Aragon. It was preserved among the subsidiary titles of his successors, and was regularly included in the full title of the Spanish monarchs at least until the takeover of the Spanish crown by the House of Bourbon.
In 1378-79, the Catalans lost most of their possessions in Boeotia to the Navarrese Company, while from the south the ambitious Florentine adventurer Nerio Acciaioli, lord of Corinth, took over Megara in 1374 and began applying pressure on Athens. By 1380, the Catalans were left only with the two capitals of Athens and Neopatras, as well as the County of Salona. Athens fell to Acciaioli in 1388, and in 1390 he captured Neopatras as well. Acciaioli could boast in the title "Lord of Corinth and the Duchy of Athens and Neopatras", but his triumph was short-lived: in 1393/4 the Ottoman Turks conquered Neopatras and the entire Spercheios River valley.