Due to Istanbul's unique geography and the depth of the Bosporus strait which divides the city, the European and Asian metro networks do not connect directly.

The two parts of the city are linked through the Marmaray commuter rail line, which is connected to the metro in several places.

In addition to the Marmaray commuter rail, the metro connects to the F1, Tünel (F2), F3 and F4 funicular lines and with the network of the Istanbul Tram,[5] Metrobüs and the cable cars.

The oldest underground urban rail line in Istanbul is the Tünel, which entered service on 17 January 1875.

The first master plan for a full metro network in Istanbul, titled Avant Projet d'un Métropolitain à Constantinople and conceived by the French engineer L. Guerby, dates to 10 January 1912.

[8] The plan comprised a total of 24 stations between the Topkapı and Şişli districts and included a connection through the Golden Horn.

In 1936 the French urban planner Henri Prost proposed a metro network between the districts of Taksim and Beyazıt, to the north and south of the Golden Horn, respectively.

[9][10] In October 1951 the Dutch firm Nedeco proposed a similar route between Taksim and Beyazıt, and in September 1952 the Director of the Paris Transportation Department, Marc Langevin, prepared a 14-chapter report together with his associate Louis Meizzonet for the implementation of the project and its integration with the other means of public transportation in the city.

Taking into account the seismic activity in Istanbul, the entire network was built with the cut-and-cover method[citation needed] to withstand an earthquake of up to 9.0 on the Richter magnitude scale.

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.

[17] The southern extension of the M2 line from Taksim to Yenikapı, across the Golden Horn with Haliç station on the bridge and underground through the historic peninsula, entered service on 15 February 2014.

)[19][20] The total length of the European side of the M2 line will reach 23 km (14.29 mi) when all 16 stations from Hacıosman to Yenikapı will be completed;[21][22][23] not including the 93-metre (305 ft 1 in)-long Golden Horn Metro Bridge,[24] the 0.6 km (0.37 mi) long Taksim-Kabataş tunnel connection with the Seabus port,[25] and the 0.6 km (0.37 mi) long Yenikapı-Aksaray tunnel connecting the M1 line to the Yenikapı Transfer Center.

[23] On the Asian side, construction is in progress of the remaining portion of the 26.5 km (16.47 mi) long M4 line from Kadıköy to Kaynarca, yielding a total of 19 stations.

Construction of the 20 km (12.43 mi) long M5 line from Üsküdar via Ümraniye to Çekmeköy started in March 2012.

Frutiger LT Pro is used as the font for the icons.The Istanbul Metro system has a total of 159 stations in operation with 35 more under construction.

Inside the mezzanines are ticket machines and turnstiles, where passengers must pay to enter fare control zones and proceed to the trains.

[51][52] In some stations, mezzanines connect directly to nearby buildings and structures, such as shopping malls or business centres.

Each station concourse or mezzanine are patrolled by Istanbul Metro security guards to prevent fare evasion and crime.

Stations with large walkways toward different exits, such as Taksim, also have travelators to cover the long walking distances.

The oldest platforms of the network, built between 1989 and 2002 on the M1 line, are 100 m (328 ft 1 in) and can accommodate trains up to 4 cars long.

Platforms of stations on the M1 line are supported by square and tiled central columns (e.g. Aksaray, Emniyet - Fatih and Topkapı - Ulubatlı.)

The M4 line has a vapur (traditional ferry), motorboat, İDO and nostalgic tram interchange at Kadıköy which is the heart of Istanbul's Asian side.

These trains are air-conditioned and equipped with LCD screens, and share a similar exterior design to the first three generations of rolling stock used on the Caracas Metro in Venezuela.

On 30 January 2009, the first 8 trains (each with 4 wagons) built by Eurotem (the Turkish factory of Hyundai Rotem) entered service.

[55] In September 2009, CAF signed a contract to supply 144 units for the M4 metro line, amounting to 1.1 million euros.

These metro units are formed with 4 cars for a total length of 90 meters and have a maximum transport capacity of 1300 passengers.

[56] In August 2013, tender for the 126 driverless train units for the M5 line was won by CAF and Mitsubishi with 119 million euros.

[58] In March 2016, Eurotem signed a contract to supply 300 driverless units for the M7 line, amounting to 280.200.000 euros.

The rolling stock on the M3 line, consists of 68 Alstom Metropolis AM4 (similar-looking vehicles are used at M4 Budapest Metro) units.

In 2019, The Ministry of Transport and Infrastructure began the planning of a 30.2 km (18.8 mi) line that would link İncirli with Söğütlüçeşme via a tunnel under the Bosphorus also designed to accommodate road traffic.