Vefa Church-Mosque (Turkish Vefa Kilise Camii/Molla Gürani Camii) was a Middle Byzantine church in Constantinople, north of the Valens of Aqueduct. It is a typical cross-in-square with a tripartite bema, a nine-bay naos with the central bay topped by an elegant dome, and a three-bay narthex. While it has traditionally been identified as the church of St. Theodore, its identity is uncertain. It seems that it was converted into a mosque by Sheikh al-Islam Mullah Gürani during the reign of Mehmet II or Beyazid II.
It probably dates to the 11th or 12th century. Several additions were made in the Palaiologan era (perhaps in the 13th century), the most important of which was a five-bay outer narthex with three domes. A belfry, whose base survives, was added at the same period in the southwestern corner of the building. The two-story annex on the north side predates the construction of the exonarthex. A similar structure is found in the Monastery of Chora. Nineteenth-century drawings show that there was a chapel or a colonnaded portico, which has since disappeared, attached to the south of the church. It was accessed by a large tripartite opening, which is now blocked by masonry. The date of this structure is debated. 
The exonarthex preserves some of its original mosaic decoration (dating to the Palaiologan era). The apex of the southern dome has an image of the Theotokos and Christ child with eight ancestors of Christ in the flutes of the dome. Fragmentary mosaics were also found in the central dome.