The siege of Sinope in 1214 was a successful siege and capture of Sinope by the Sultanate of Rum under their Sultan, Kaykaus I (r. 12111220). Sinope was an important port city on the Black Sea coast of modern Turkey, at the time held by the Empire of Trebizond, one of the Byzantine Greek successor states formed after the Fourth Crusade. The siege is described in some detail by the near-contemporary Seljuq chronicler Ibn Bibi. The Trapezuntine emperor Alexios I (r. 12041222) led an army to break the siege, but he was defeated and captured, and the city surrendered on 1 November.

Sinop, historically known as Sinope (; Greek: Σινώπη, romanized: Sinōpē), is a city on the isthmus of İnce Burun (İnceburun, Cape Ince), near Cape Sinope (Sinop Burnu, Boztepe Cape, Boztepe Burnu) which is situated on the northernmost edge of the Turkish side of the Black Sea coast, in the ancient region of Paphlagonia, in modern-day northern Turkey. The city serves as the capital of Sinop Province.