The Tube: 150 years and counting
Today around 3.5million journeys are made on the network each day, across 11 lines serving 270 stations.
Here is our potted history of the Tube:
The early years
1863: The London Metropolitan Railway opens, stretching just under four miles.
Steam trains chug between Paddington and Farringdon Street on what is now the Circle line, carrying an average of 26,500 passengers a day during its first three months.
1868: The Metropolitan District Railway from South Kensington to Westminster (now part of the District and Circle lines) is launched.
1884: The circle is 'completed' by linking the Metropolitan and District lines at both ends.
1890: The world's first deep-level electric railway opens between King William Street (now Monument/Bank station) and Stockwell.
It forms part of what is now the Northern line.
1898: The one-stop Tube link between Waterloo and the City (affectionately known as 'The Drain') is built.
New century, new lines
1900: The Central London Railway opens between Shepherd's Bush and Bank.
It was dubbed the 'Twopenny Tube' due to the flat fare of two pence for tickets between any two stations.
1906: The first section of the Piccadilly line opens, running between Finsbury Park and Hammersmith.
The Bakerloo line, between Baker Street and Waterloo, also opens in the same year.
1907: What is now the Charing Cross branch of the Northern line opens, with two northern spurs going as far as Highgate (Archway) and Golders Green.
1911: Earl's Court becomes the first Tube station with escalators.
1935-40: The Bakerloo and Northern lines are extended.
1908: The Underground name appeared at stations and the iconic roundel was born.
1929: The Underground's new headquarters at 55 Broadway opens.
1933: Harry Beck's famous Underground map appears for the first time and is now used as a template for metro networks across the world.
1914-18: During the First World War women take over many roles left vacant as men join the army.
They are known as 'wartime substitutes'.
1939-45: Tube station platforms are used as air raid shelters during World War Two.
The Piccadilly line's Holborn to Aldwych branch closes and is used to store treasures from the British Museum.
1969: The Victoria line opens between Brixton and Walthamstow Central.
1979: The Jubilee line starts operating between Stanmore and Charing Cross.
1986: Heathrow's new Terminal 4 leads to the opening of a Piccadilly line extension.
1999: The Jubilee line extension between Green Park and Stratford opens.
1961: The network is fully electrified.
1983: Dot matrix train/destination indicators are introduced on platforms.
1986: Fare zone and the Travelcard are launched.
2003: The Oyster card ticketing system is introduced.
Present and future
A huge programme of investment and upgrade is now under way on the Tube.
Major improvements were made ahead of the Olympics - the Jubilee and Victoria lines now have more frequent and reliable services and King's Cross and Green Park stations were transformed.
As London continues to grow, so does the need to increase capacity and improve services on the Tube network.
New air-conditioned trains are being introduced on 40 per cent of the network, and the Northern line is set for major improvements.
More stations are becoming step-free, and there are plans for an extension of the Northern line to Battersea, including two new stations.
Find out more at tfl.gov.uk/tup