Sea transport is vital for Istanbul, as the city is practically surrounded by sea on all sides: the Sea of Marmara, the Golden Horn, the Bosphorus and the Black Sea. Many Istanbulites live on the Asian side of the city but work on the European side (or vice-versa) and the city's famous commuter ferries form the backbone of the daily transition between the two parts of the city – even more so than the two suspension bridges which span the Bosphorus. The commuter ferries, along with the high speed catamaran Seabus (Deniz Otobüsü), also form the main connection between the city and the Princes' Islands.

The first steam ferries appeared on the Bosphorus in 1837 and were operated by private sector companies.On 1 January 1851, the Şirket-i Hayriye (literally the Goodwill Company, as the Istanbul Ferry Company was originally called) was established by the Ottoman state. The Şirket-i Hayriye continued to operate the city's landmark commuter ferries until the early years of the Republican period, when they went under the direction of Türkiye Denizcilik İşletmeleri (Turkish State Maritime Lines). Since March 2006, Istanbul's traditional commuter ferries are being operated by İstanbul Deniz Otobüsleri (Istanbul Sea Buses) which also operates the high speed catamaran Seabus.

İDO (İstanbul Deniz Otobüsleri – Istanbul Sea Buses) was established in 1987 and operates the high speed catamaran Seabus which run between the European and Asian parts of Istanbul, also connecting the city with the Princes' Islands and other destinations in the Sea of Marmara. The Yenikapı High Speed Car Ferry Port on the European side, and the Pendik High Speed Car Ferry Port on the Asian side, are where the high speed catamaran "car ferries" are based. The car ferries which operate between Yenikapı (on the European side of Istanbul) and Bandırma reduce the driving time between Istanbul and İzmir and other major destinations on Turkey's Aegean coast by several hours; while those which operate between Yenikapı or Pendik (on the Asian side of Istanbul) and Yalova significantly reduce the driving time between Istanbul and Bursa or Antalya.

The port of Istanbul is the most important one in the country. The old port on the Golden Horn serves primarily for personal navigation, while Karaköy port in Galata is used by the large cruise liners. Regular services as well as cruises from both Karaköy and Eminönü exist to several port cities in the Mediterranean Sea and Black Sea. Istanbul's main cargo port is located in the Harem district on the Asian side of the city. Istanbul also has several marinas of varying size for personal navigation, the largest of which are the Ataköy Marina on the European side and Kalamış Marina on the Asian side.

Motorways

Fatih Sultan Mehmet Bridge. The State Road D.100 and the European route E80, the Trans European Motorway (TEM) O-3 are the two main motorway connections between Europe and Turkey. The motorway network around Istanbul is well developed and is constantly being extended. Motorways lead east to Ankara and west to Edirne. There are also two express highways circling the city. The older one, the O-1, is mostly used for inner city traffic; while the more recent one, the O-2, is mostly used by intercity or intercontinental traffic.
Büyükdere Avenue runs through the heart of Levent and Maslak.

The Bosphorus Bridge on the O-1 and the Fatih Sultan Mehmet Bridge on theO-2 establish the motorway connection between the European and the Asian sides of the Bosphorus. The southern and northern shores of the Golden Horn, an inlet of the Bosphorus on the European side of the city, are connected through the Galata Bridge, the Atatürk Bridge and the Haliç Bridge; the latter also being a part of the O-1 motorway network.

Büyükdere Avenue is the main artery that runs through the central business districts of Levent and Maslak on the European side, and is also accessible through a number of subway stations. At the point where the O-1 motorway junctions and tunnels between the quarters of Gayrettepe and Zincirlikuyu come together, Büyükdere Avenue connects with Barbaros Boulevard, which descends towards the ferry port of Beşiktaş. There it connects with the coastal highway that runs along the European shore of the Bosphorus, from Eminönü in the south to Sarıyer in the north.

Railways

Sirkeci Terminal was opened in 1890 as the final destination terminus of the Orient Express.

In 1883, a Belgian entrepreneur, Georges Nagelmackers, began a rail service between Paris and Constantinople, using a steamship to ferry passengers from Varna to Constantinople. In 1889, a rail line was completed going through Bucharest to Constantinople, making the whole journey via land possible. The route was known as the Orient Express, made even more famous by the works of Agatha Christie and Graham Greene.

Today, the Sirkeci Terminal of the Turkish State Railways (TCDD), which was originally opened in 1890 as the terminus of the Orient Express, is the terminus of all the lines on the European side and the main connection node of the Turkish railway network with the rest of Europe. Currently, international connections are provided by the line running between Istanbul and Thessaloniki, Greece, and the Bosphorus Express serving daily between Sirkeci and Bucharest, Romania. Lines to Sofia, Belgrade, Budapest, and Chişinău are established over the Bosphorus Express connection to Bucharest.

Beyond the Bosphorus, the Haydarpaşa Terminal on the Asian side serves lines running several times daily to Ankara, and less frequently to other destinations in Anatolia. The railway networks on the European and Asian sides are currently connected by the train ferry across the Bosphorus, which will be replaced by an underwater tunnel connection with the completion of the Marmaray project, scheduled for 2012. Marmaray (Bosphorus Rail Tunnel) will also connect the metro lines on the European and Asian parts of the city. Inaugurated in 1908, the Haydarpaşa Terminal was originally opened as the terminus of the Istanbul-Konya-Baghdad and Istanbul-Damascus-Medina railways.

A railway line runs between the main train station of the European part, the Sirkeci Terminal, and the Halkalı district towards the west of the city centre, with 18 stations along its 30 km length. A single trip takes 48 minutes. Another suburban line runs on the Anatolian part from the main train station, the Haydarpaşa Terminal, to Gebze at the eastern end of the city. The 44 km long line has 28 stations and the trip takes 65 minutes. 720,000 passengers use the urban rail lines on the European side of the city every day.

Trams

A modern tram running in the Galata quarter of Istanbul.

Trams first entered service in Istanbul on 3 September 1869, at the Tophane – Ortaköy line. In 1871 the Azapkapı – Galata; Aksaray – Yedikule; Aksaray – Topkapı; and Eminönü – Aksaray lines entered service. Other lines which entered service in the late 19th century included the Voyvoda Caddesi – Kabristan Sokağı – Tepebaşı – Taksim – Pangaltı – Şişli line; the Bayezid – Şehzadebaşı line; the Fatih – Edirnekapı – Galatasaray – Tünel line; and the Eminönü – Bahçekapı line. Since 1939 the trams of the city are operated by the İETT. On 12 August 1961, the historic red trams of Istanbul were removed from the city's European side; and on 14 November 1966, they were removed from the city's Asian side. Towards the end of 1990, replicas of these historic red trams were put in service along the İstiklal Avenue between Taksim and Tünel, which is a single 1.6 km-long (1640 m) line. On 1 November 2003, another nostalgic tram line (T3) was reopened on the Anatolian part of Istanbul between Kadıköy and Moda. It has 10 stations on a 2.6 km long route. The trip takes 21 minutes.

A fast tram (T1) was put in service in 1992 on standard gauge track with modern cars, connecting Sirkeci with Topkapı. The line was extended on one end from Topkapı to Zeytinburnu in March 1994, and on the other end from Sirkeci to Eminönü in April 1996. On 30 January 2005 it was extended from Eminönü to Fındıklı, crossing the Golden Horn through the Galata Bridge for the first time after 44 years. A final extension to Kabataş was opened in June 2006. The line has 24 stations on a length of 14 km. Service was initially operated with 22 LRT vehicles built by ABB, now reassigned to other lines; while stations were provided with temporary high platforms. These vehicles were replaced by 55 low-floor Bombardier Flexity Swift trams in 2003. An entire trip takes 42 minutes. The daily transport capacity is 155,000 passengers. The amount of investment totaled US$110 million. In September 2006, a second tram line (T2) was added, running west from Zeytinburnu to Bağcılar. Service on this line is operated with 14 ABB LRT cars. Stations have high platforms at the level of the car floor.

Funiculars

The modern funicular line running between Kabataş and Taksim.

Istanbul is served by two underground funicular railways, of very different ages and styles. The older of these lines is the Tünel (1875). Inaugurated on 17 January 1875, the Tünel is the second-oldest subterranean urban rail line in the world after the London Underground (1863) (arguably third in the world, if one counts Brooklyn, New York's abandoned Atlantic Avenue Tunnel) and the first subterranean urban rail line in continental Europe; though the first full subway line with multiple underground stations in continental Europe was the Line 1 of the Budapest Metro (1896). The Tünel is 573 m (1,879.92 ft) long with an altitude difference of 60 m and no intermediate stations between Karaköy and Tünel Square. It has been continuously in service since 1875. Two trains run on a single rail every 3.5 minutes, and a trip takes 1.5 minutes. Making 64,800 trips, totaling 37,066 kilometres a year, the Tünel carries 15,000 passengers per day.

A second funicular line, the Kabataş-Taksim Funicular, entered service on 29 June 2006, connecting Kabataş and Taksim. This system connects the Seabus station and the tram stop in Kabataş to the metro station at Taksim Square. It is about 600 meters long and climbs approximately 60 meters in 110 seconds, carrying 9,000 passengers per day.

Light rail

Main article: Istanbul LRT

The Istanbul LRT is a light rail transit system consisting of 2 lines. The first line (M1) began service on 3 September 1989 between Aksaray and Kartaltepe. The line was further developed step-by-step and reached Atatürk Airport on 20 December 2002. The other line (T4) was opened in 2007 between Edirnekapı and Mescid-i Selam. There are 36 stations, including 12 underground and 3 viaduct stations, on the line's 32 km length. The lines are totally segregated from other traffic, without level crossings, and run underground for 10.4 km. Service is operated with LRT vehicles built by ABB in 1988.
Metro
Main article: Istanbul Metro
Levent subway station.

Construction works of the Istanbul Metro (M2) began in 1992 and the first completed section between Taksim and 4. Levent entered service on 16 September 2000. This section of the line is 8.5 km (5.3 mi) long and has 6 stations. In 2000, there were 8 Alstom-built 4-car train sets in service, which ran every 5 minutes on average and transported 130,000 passengers daily. On 30 January 2009, the first train sets built by Eurotem entered service. Eurotem will build a total of 92 new wagons for the M2 line. As of 30 January 2009, a total of 34 train sets, each with 4 cars, were being used on the M2 line.

A northern extension from 4. Levent to Maslak was opened on 30 January 2009. The southern extension of the M2 line from Taksim to Yenikapı, across the Golden Horn on a bridge and underground through the historic peninsula, has thus far been completed up to the Şişhane station in Beyoğlu, which also entered service on 30 January 2009. At Yenikapı the M2 network will intersect with the extended light metro and suburban train lines, and with the Marmaray tunnel.

At present, the M2 line has 10 stations in service on the European side of the city; while 6 new stations on the European side and 16 new stations on the Asian side are currently under construction. The trip between the Şişhane station in Beyoğlu and the Atatürk Oto Sanayi station in Maslak is 15.65 km (9.7 mi) long and takes 21 minutes. The total length of the European side of the M2 line will reach 18.36 km (11.4 mi) when all 16 stations from Hacıosman to Yenikapı will be completed; not including the 936 metres long Golden Horn metro bridge, the 0.6 km long Taksim-Kabataş tunnel connection with the Seabus port, the 0.6 km long Yenikapı-Aksaray tunnel connection with the LRT network, and the 13.6 km long Marmaray tunnel.

On the Asian side, construction of the 21.66 km (13.5 miles) long M2 line from Kadıköy to Kartal continues, which will have a total of 16 stations.[106] The Marmaray tunnel (Bosporus undersea railway tunnel) will connect the metro lines of the Asian and European parts of the city. According to the scheduled construction timeline, the tunnel will enter service in 2012.