The Istanbul Metro is a rapid transit railway network serving the city of Istanbul, Turkey. Apart from the M11 line, which is operated by TCDD Taşımacılık, the system is operated by Metro Istanbul, a public enterprise controlled by the Istanbul Metropolitan Municipality. The oldest section of the metro is the M1 line, which opened in 1989. As of April 2023, the system now consists of 137 stations in service, and 56 more are under construction. The system consists of eleven lines: lines designated M1A, M1B, M2, M3, M6, M7, M9 and M11 are on the European side of the Bosporus, while lines M4, M5 and M8 are on the Asian side. Due to Istanbul's unique geography and the depth of the Bosporus Strait that divides the city, the European and Asian metro networks do not connect directly. Both parts of the city are connected via the Marmaray Commuter Rail Line, which is connected to the metro in many places. Three metro lines are under construction in the Asian part: M10, M12 and M14. Additionally, expansion work is underway on the M3, M7, M9 and M11 lines and the M4 and M5 lines. The Istanbul Metro not only reduces traffic congestion, but also serves as a lifeline for millions of Istanbulites, demonstrating the city's commitment to efficient, accessible and sustainable urban transportation.