The Green Line is the oldest of the three Stockholm Metro lines. The 41.256-kilometre (25.635 mi) long line comprises a single double-tracked line north of the city centre, splitting into three branches south of the city centre. The first section of the line opened as a metro in 1950, making it the first and oldest metro line in the Nordic countries, although some parts of the line date back to the 1930s and were originally used by the Stockholm tramway.

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.