The Duchy of Athens (Greek: Δουκᾶτον Ἀθηνῶν, Doukaton Athinon; Catalan: Ducat d'Atenes) was one of the Crusader states set up in Greece after the conquest of the Byzantine Empire during the Fourth Crusade as part of the process known as Frankokratia, encompassing the regions of Attica and Boeotia, and surviving until its conquest by the Ottoman Empire in the 15th century.

The first duke of Athens (as well as of Thebes, at first) was Otto de la Roche, a minor Burgundian knight of the Fourth Crusade.

The Duchy occupied the Attic peninsula as well as Boeotia and extended partially into Thessaly, sharing an undefined border with Thessalonica and then Epirus.

Walter hired the Catalan Company, a group of mercenaries founded by Roger de Flor, to fight against the Byzantine successor state of Epirus, but when he tried to dismiss and cheat them of their pay in 1311, they slew him and the bulk of the Frankish nobility at the Battle of Halmyros and took over the Duchy.

Under Aragonese rule, the feudal system continued to exist, not anymore under the Assizes of Romania, but under the Customs of Barcelona, and the official common language was now Catalan instead of French.

It was a metropolitan see (province or eparchy) with eleven suffragans at the time of conquest: Euripus, Daulia, Coronea, Andros, Oreos, Scyrus, Karystos, Porthmus, Aulon, Syra and Seriphus, and Ceos and Thermiae (or Cythnus).

The archiepiscopal offices of Athens and Thebes were held by Frenchmen and Italians until the late fourteenth century, when Catalan or Aragonese people began to fill them.

Of Burgundian origin, the dukes of the petty lordly family from La Roche renewed the ancient city of Plato and Aristotle as a courtly European capital of chivalry.

The conquest of the duchy by the Catalan Company and subsequent annexation to Aragon came after a disputed succession following the death of the last Burgundian duke.

The Catalans recognised the king of Sicily as suzerain and this left the duchy often as an appanage in the hands of younger sons and under vicars general.

In Dante's Divine Comedy (especially in Inferno), there are many references to Pelasgian mythology, and the poet connects them to Late Middle Ages Balkans, such as with the Duke of Athens.