Kalenderhane Mosque (Turkish: Kalenderhane Camii) is a former Eastern Orthodox church in Istanbul, converted into a mosque by the Ottomans. With high probability the church was originally dedicated to the Theotokos Kyriotissa. The building is sometimes referred to as Kalender Haneh Jamissi and St. Mary Diaconissa. This building represents one among the few extant examples of a Byzantine church with domed Greek cross plan.
The mosque is located in the Fatih district of Istanbul, Turkey, in the picturesque neighborhood of Vefa, and lies immediately to the south of the easternmost extant section of the aqueduct of Valens, and less than one km to the southeast of the Vefa Kilise Mosque.