The War of the Euboeote Succession is fought in 1256–1258 between the Prince of Achaea, William II of Villehardouin, and a broad coalition of other rulers from throughout Frankish Greece who feel threatened by William's aspirations.

The war is sparked by William's attempt to gain control of a third of the island of Euboea, which is resisted by the local Lombard barons ("terciers" or "triarchs") with the aid of the Republic of Venice.

The Lord of Athens and Thebes, Guy I de la Roche, also enters the war against William, along with other barons of Central Greece.

Their defeat at the Battle of Karydi in May/June 1258 effectively brings the war to an end in an Achaean victory, although a definite peace treaty is not concluded until 1262.