Fenâri Îsâ Mosque (full name in Turkish: Molla Fenâri Îsâ Câmîi), known in Byzantine times as the Lips Monastery (Greek: Μονὴ τοῦ Λιβός), is a mosque in Istanbul, made of two former Eastern Orthodox churches.

The place of worship is located on Adnan Menderes Boulevard, also known as Vatan Street, in the Fatih district of Istanbul. It is between the Fatih-Emniyet and Aksaray stops on the M1 line of the Istanbul Metro; It can also be easily reached from IETT's İskenderpaşa or Oğuzhan stops.

In 908, the Byzantine admiral Constantine Lips inaugurated a nunnery in the presence of the Emperor Leo VI the Wise (r. 886–912). The nunnery was dedicated to the Virgin Theotokos Panachrantos ("Immaculate Mother of God") in a place called "Merdosangaris" (Greek: Μερδοσαγγάρης), in the valley of the Lycus (the river of Constantinople). The nunnery was known also after his name (Monē tou Libos), and became one of the largest of Constantinople.

The church was built on the remains of another shrine from the 6th century, and used the tombstones of an ancient Roman cemetery. Relics of Saint Irene were stored here. The church is generally known as "North Church".

After the Latin invasion and the restoration of the Byzantine Empire, between 1286 and 1304, Empress Theodora, widow of Emperor Michael VIII Palaiologos (r. 1259–1282), erected another church dedicated to St. John the Baptist (Ἐκκλησία τοῦ Ἁγίου Ἰωάννου Προδρόμου τοῦ Λιβός) south of the first church. Several exponents of the imperial dynasty of the Palaiologos were buried there besides Theodora: her son Constantine, Empress Irene of Montferrat and her husband Emperor Andronikos II (r. 1282–1328). This church is generally known as the "South Church". The Empress restored also the nunnery, which by that time had been possibly abandoned. According to its typikon, the nunnery at that time hosted a total of 50 women and also a Xenon for laywomen with 15 beds attached.

During the 14th century an esonarthex and a parekklesion were added to the church. The custom of burying members of the imperial family in the complex continued in the 15th century with Anna, first wife of Emperor John VIII Palaiologos (r. 1425–1448), in 1417. The church was possibly used as a cemetery also after 1453.

In 1497–1498, shortly after the Fall of Constantinople and during the reign of Sultan Beyazid II (1481–1512), the south church was converted into a mescit (a small mosque) by the Ottoman dignitary Fenarizade Alâeddin Ali ben Yusuf Effendi, Qadi 'asker of Rumeli, and nephew of Molla Şemseddin Fenari, whose family belonged to the religious class of the ulema. He built a minaret in the southeast angle, and a mihrab in the apse. Since one of the head preachers of the madrasah was named Îsâ ("Jesus" in Arabic and Turkish), his name was added to that of the mosque. The edifice burned down in 1633, was restored in 1636 by Grand Vizier Bayram Pasha, who upgraded the building to cami ("mosque") and converted the north church into a tekke (a dervish lodge). In this occasion the columns of the north church were substituted with piers, the two domes were renovated, and the mosaic decoration was removed. After another fire in 1782, the complex was restored again in 1847/48. In this occasion also the columns of the south church were substituted with piers, and the balustrade parapets of the narthex were removed too. The building burned once more in 1918, and was abandoned. During excavations performed in 1929, twenty-two sarcophagi have been found. The complex has been thoroughly restored between the 1950s and 1960s by the Byzantine Institute of America, and since then serves again as a mosque.

The north church has an unusual quincuncial (cross-in-square) plan, and was one of the first shrines in Constantinople to adopt this plan, whose prototype is possibly the Nea Ekklesia ("New Church"), erected in Constantinople in the year 880, of which no remains are extant. During the Ottoman period the four columns have been replaced with two pointed arches which span the whole church.