Northern Line

The Northern line is a line on the underground railway system, London Underground. It is coloured black on the Tube map.

For most of its length it is a deep-level tube line. The line carries about 252,310,000 passengers per year, making it the second busiest line in the Underground system. It is unique in having two different routes through central London. Despite its name, it does not serve the northernmost stations on the network, although it does serve the southernmost station (Morden tube station) as well as 16 of the system's 29 stations south of the River Thames. There are 50 stations on the line, 36 of them below ground.

The line has a complicated history, and the current complex arrangement of two northern branches, two central branches and the southern branch reflects its genesis as three separate railway companies that were combined in the 1920s and 1930s. An extension in the 1920s used a route originally planned by a fourth company. Abandoned plans dating from the 1920s, to extend the line further southwards, and then northwards in the 1930s, would have incorporated parts of the routes of two further companies. From the 1930s to the 1970s, the tracks of a seventh company were also managed as a branch of the Northern line.