The Mass Transit Railway (MTR) is a major public transport network serving Hong Kong. Operated by the MTR Corporation Limited (MTRCL), it consists of heavy rail, light rail, and feeder bus service centred on a 10-line rapid transit network serving the urbanised areas of Hong Kong Island, Kowloon, and the New Territories. The system included 230.9 km (143.5 mi) of rail in 2018 with 165 stations, including 97 heavy rail stations and 68 light rail stops.Under the government's rail-led transport policy, the MTR system is a common mode of public transport in Hong Kong, with over five million trips made in an average weekday. It consistently achieves a 99.9 per cent on-time rate on its train journeys. As of 2018, the MTR has a 49.3 per cent market share of the franchised public transport market, making it the most popular transport option in Hong Kong. The integration of the Octopus smart card fare-payment technology into the MTR system in September 1997 has further enhanced the ease of commuting on the MTR.

Construction of the MTR was prompted by a study, released in 1967, commissioned by the Government of British Hong Kong to find solutions to the increasing road congestion problem caused by the territory's fast-growing economy. Construction started soon after the release of the study, and the first line opened in 1979. The MTR was immediately popular with residents of Hong Kong; as a result, subsequent lines have been built to cover more territory. There are continual debates regarding how and where to expand the MTR network.The MTR has served as a model for some newly built systems, particularly in Mainland China.