The Stockholm Metro is a rapid transit system in Stockholm, Sweden. The first line opened in 1950 as the first metro line in the Nordic countries, and today the system has 100 stations in use, of which 47 are underground and 53 above ground. There are three coloured lines, as shown on the tube maps, which form seven numbered routes with different termini. Routes numbered 17, 18 and 19, 13 and 14 and 10 and 11 all go through the centre of the city, resulting in a very centralized system. All three lines and seven routes interchange at T-Centralen station. Apart from this, there are three other interchange between lines, at Fridhemsplan, Slussen and Gamla stan stations.

Stockholm is the capital and most populous city of Sweden as well as the largest urban area in the Nordic countries. Approximately 1 million people live in the municipality, with 1.6 million in the urban area, and 2.4 million in the metropolitan area. The city stretches across fourteen islands where Lake Mälaren flows into the Baltic Sea. Outside the city to the east, and along the coast, is the island chain of the Stockholm archipelago. The area has been settled since the Stone Age, in the 6th millennium BC, and was founded as a city in 1252 by Swedish statesman Birger Jarl. The city serves as the county seat of Stockholm County.