Lagos Rail Mass Transit is a rapid transit system in Lagos State. The rail system is managed by the Lagos Metropolitan Area Transport Authority (LAMATA). The railway equipment including electric power, signals, rolling stock, and fare collection equipment is provided by the private sector under a concession contract. LAMATA is responsible for policy direction, regulation, and infrastructure for the network. The first section of the network, Phase I of the Blue Line, was originally planned to be completed in 2011, though the construction has suffered many delays caused by shortage of funds and change of government. The Blue Line opened on September 4, 2023 and the Red Line opened on October 15, 2024.

The idea of developing a rapid transit in Lagos state dates back to 1983 with the Lagos Metroline network conceived by Alhaji Lateef Jakande during the Second Nigerian Republic. The initial Metroline project was scrapped in 1985 by Muhammadu Buhari at a loss of over $78 million to state tax payers. In 2003, then-governor Bola Tinubu revived the rail network for Lagos State with a formal announcement of its construction. An initial cost of $135 million was proposed for the Greater Lagos Urban Transportation Project to be implemented by the newly formed LAMATA. LAMATA initially concentrated on developing a Bus Rapid Transit system, running from Mile 2 to Lagos Island. In 2008, LAMATA began focusing on the Blue Line and the Red Line.

In September 2011, LAMATA announced that it would acquire some H5-series subway trains formerly used by the Toronto Transit Commission (TTC) for the Blue Line. The cars were to be refurbished in the United States and converted to standard gauge before being imported and put into service on the Blue and Red lines. The same contract also included an option for some H6-series subway cars from the TTC, however this has since been cancelled.

In January 2015, LAMATA opted for Chinese-built trains instead, ordering 15 electro-diesel multiple units from CRRC Dalian with an option for 14 more. About 76 H5 cars that had been taken for refurbishment to Buffalo, New York, have been scrapped by August 2015.

In August 2018, LAMATA signed an agreement with Alstom. As a part of the agreement, Alstom conducted a review of the rail lines, and electrification of a portion of the track was planned.

In January 2022, Lagos State Governor Babajide Sanwo-Olu visited the US state of Wisconsin, to purchase two Talgo VIII trainsets for service on the Red Line. They had been ordered by Wisconsin for use on the Amtrak Hiawatha in 2009, but were never placed in service, and were instead stored. Talgo VIII cars are based on the unique technology of the Talgo Pendular model, which (similar to a bicycle rider) leans into a curve resulting in less sideways force and a higher comfort for passengers when driving over a curvy track. The "leaning" of the car is passive i.e. it happens purely by the resulting force, without electronics, sensors or engines.

In 2023, LAMATA bought 11 Class 43 locomotives and 11 Mark 3 coaches from the UK. Some of the Class 43s will be used to haul rakes of the Mark 3 coaches, while others will be used to haul the Talgo rakes.

The Blue Line is the first line in the system and opened its first five stations on September 4, 2023. The entire planned route is 27 kilometres (17 mi) from Okokomaiko to Lagos Marina. Construction had been delayed due to lack of funds and was split into multiple phases.