One of the great historic cities of the world, Istanbul is the chief city and seaport of Turkey as well as its commercial, industrial, and financial center. Manufactures include textiles, glass, shoes, motor vehicles, ships, and cement. The European part of Istanbul is the terminus of an international rail service (formerly called the Orient Express), and at Haydarpaşa station, on the Asian side, begins the Baghdad Railway. Yeşilköy International Airport is nearby.

Always a cosmopolitan city, Istanbul has preserved much of its international and polyglot character and contains sizable foreign minorities. The city experienced explosive population growth in the 1970s and 80s (it tripled in size), with the Turkish Muslim majority increasing. The present administrative districts of Istanbul include Fatih and Eminönü on the European side and Kadiköy (ancient Chalcedon) and Üsküdar (Scutari) on the Asian side. Massive efforts have been made to keep up with recent growth by modernizing the city's infrastructure and municipal services. In 1973 the European and Asian sections of the city were linked by the opening of the Bosporus Bridge, one of the world's longest (3,524 ft/1,074 m) suspension bridges. This was followed by the Second Bosporus Bridge (3,322 ft/1,012 m), completed in 1988. The first section of a new subway system opened in Sept., 2000.

Istanbul is the seat of Istanbul Univ. (founded 1453 as a theological school; completely reorganized 1933), a technical university, Univ. of the Bosporus (formerly Robert College), Marmara Univ., Mimar Sinan Univ., and Yildiz Univ. It is the see of the patriarch of the Greek Orthodox Church, of a Latin-rite patriarch of the Roman Catholic Church, and of a patriarch of the Armenian Church.

The city is visited by many tourists and is a popular resort. The environs of Istanbul, particularly the villas, gardens, castles, and small communities along the Bosporus, are famed for their beauty. The part of Istanbul corresponding to historic Constantinople is situated entirely on the European side. It rises on both sides of the Golden Horn, an inlet of the Bosporus, on one of the finest sites of the world, and like Rome is built on seven hills. Several miles of its ancient moated and turreted walls are still standing. Outside the walls and N of the Golden Horn are the commercial quarter of Galata, originally a Genoese settlement; the quarter of Beyoğlu (formerly Pera), which under the Ottoman sultans was reserved for foreigners and their embassies; and Hasköy, the Jewish quarter.

The Golden Horn is crossed by two bridges, the new Galata Bridge (which replaced the famous old Galata Bridge) and the Atatürk Bridge. The former leads into the historic quarter of Stambul, the city's ancient core, abutting the Bosporus and the Sea of Marmara. The quarter of Phanar in the northwest, near the former site of the palace of Blachernae of the Byzantine emperors, contains the see of the Greek Orthodox Church and is inhabited mainly by Greeks. Some palace walls still stand. Excavations on the sites of the former Byzantine palaces have found fine works of art, and Istanbul has many monuments of the Byzantine past. Remains of the imperial residence, the Great Palace, were unearthed in 1998. The chief monument surviving from Byzantine times is the great Hagia Sophia. Originally a church, it was converted into a mosque after the Ottoman conquest in 1453 and is now a museum.

The city was destroyed (1509) by an earthquake and was rebuilt by Sultan Beyazid II. Turkish culture reached its height in the 16th cent. and from that period date most of its magnificent mosques, notably those of Beyazid II, Sulayman I, and Ahmed I. They all reflect the influence of the Hagia Sophia—yet are distinctly Turkish—and give the skyline of Istanbul its unique character, a succession of perfectly proportioned domes punctuated by minarets. In the gardens by the Bosporus stand the buildings of the Seraglio, the former palace of the Ottoman sultans, now a museum. The Seraglio, begun by Muhammad II in 1462, consists of many buildings and kiosks, grouped into three courts, the last of which contained the treasury, the harem, and the private apartments of the ruler. In the 19th cent. the sultans shifted (1853) their residence to the Dolma Bahçe Palace and the Yildiz Kiosk, N of Beyoğlu on the Bosporus.