The London Underground (also known simply as the Underground or as the Tube) is a rapid transit system serving Greater London and parts of the adjacent home counties of Buckinghamshire, Essex, and Hertfordshire in England. Managed by Transport for London (TfL), the network spans 11 lines and 250 miles (400 km) of track, serving 272 stations. While the system's nickname originates from its deep-level circular tunnels, only 45% of the network is underground, with the majority of the outer surface tracks located north of the River Thames. It is one of the busiest rapid transit networks in the world, accommodating over 1.2 billion passenger journeys annually in 2024–25.
The network has its origins in the Metropolitan Railway, which opened on 10 January 1863 as the world's first underground passenger railway. Early sub-surface lines used the cut-and-cover construction method, later transitioning to deeper, circular "tube" tunnels, which pioneered the use of underground electric traction with the opening of the City and South London Railway in 1890 (now part of the Northern line). Originally owned and operated by competing private companies, these distinct routes were unified under the "Underground" brand in the early 20th century and publicly consolidated in 1933 to form London Transport. The network expanded with post-war additions like the Victoria and Jubilee lines, before management was transferred in 2000 to TfL, under which the system is operated by its subsidiary, London Underground Limited.
The system is widely recognised for its influence on graphic design and corporate identity. Under the mid-20th-century leadership of the London Passenger Transport Board, the network pioneered a modernist aesthetic through its unique station architecture, iconic posters, and distinct branding assets. This design legacy includes Edward Johnston's 1916 Johnston typeface, the ubiquitous roundel logo, and Harry Beck's schematic Tube map designed in 1931, which became a global design icon and remains the framework for London's broader multi-modal transport map today.
Physically, the network is divided into sub-surface and deep-level tube lines, operated using a unique four-rail DC system. Infrastructure and operations have undergone major transformations to meet contemporary demand, including advanced signalling overhauls, the weekend Night Tube, and sweeping safety regulations implemented following the fatal King's Cross fire in 1987. Fares and ticketing have similarly evolved from the unified Travelcard (1983) and Oyster card (2003) to open-payment contactless systems introduced in 2014, a global first for a major public transport network.
The idea of an underground railway linking the City of London with the urban centre was proposed in the 1830s, and the Metropolitan Railway was granted permission to build such a line in 1854. To prepare construction, a short test tunnel was built in 1855 in Kibblesworth, a small town with geological properties similar to London. This test tunnel was used for two years in the development of the first underground train, and was later, in 1861, filled up. The world's first underground railway, it opened in January 1863 between Paddington and Farringdon using gas-lit wooden carriages hauled by steam locomotives. It was hailed as a success, carrying 38,000 passengers on the opening day, and borrowing trains from other railways to supplement the service. The Metropolitan District Railway (commonly known as the District Railway) opened in December 1868 from South Kensington to Westminster as part of a plan for an underground "inner circle" connecting London's main-line stations. The Metropolitan and District railways completed the Circle line in 1884, built using the cut and cover method. Both railways expanded, the District building five branches to the west reaching Ealing, Hounslow, Uxbridge, Richmond and Wimbledon and the Metropolitan eventually extended as far as Verney Junction in Buckinghamshire – more than 50 miles (80 km) from Baker Street and the centre of London.
While steam locomotives were in use on the Underground there were many instances of passengers collapsing while travelling, owing to heat and pollution, leading for calls to clean the air through the installation of garden plants. The Metropolitan even encouraged beards for staff to act as an air filter.
For the first deep-level tube line, the City and South London Railway, two 10 feet 2 inches (3.10 m) diameter circular tunnels were dug between King William Street (close to today's Monument station) and Stockwell, under the roads to avoid the need for agreement with owners of property on the surface. This opened in 1890 with electric locomotives that hauled carriages with small opaque windows, nicknamed padded cells. The Waterloo and City Railway opened in 1898, followed by the Central London Railway in 1900, known as the "twopenny tube". These two ran electric trains in circular tunnels having diameters between 11 feet 8 inches (3.56 m) and 12 feet 2.5 inches (3.72 m), whereas the Great Northern and City Railway, which opened in 1904, was built to take main line trains from Finsbury Park to a Moorgate terminus in the City and had 16-foot (4.9 m) diameter tunnels.
With the advent of electric Tube services (the Waterloo and City Railway and the Great Northern and City Railway), the Volks Electric Railway, in Brighton, and competition from electric trams, the pioneering Underground companies needed modernising. In the early 20th century, the District and Metropolitan railways needed to electrify and a joint committee recommended an AC system, the two companies co-operating because of the shared ownership of the inner circle. The District, needing to raise the finance necessary, found an investor in the American Charles Yerkes who favoured a DC system similar to that in use on the City & South London and Central London railways. The Metropolitan Railway protested about the change of plan, but after arbitration by the Board of Trade, the DC system was adopted.
There were reports claiming beneficial outcomes of using the Underground, including the designation of Great Portland Street as a "sanatorium for [sufferers of ...] asthma and bronchial complaints", tonsillitis could be cured with acid gas and the Twopenny Tube cured anorexia.
Underground Electric Railways Company era
Yerkes soon had control of the District Railway and established the Underground Electric Railways Company of London (UERL) in 1902 to finance and operate three tube lines, the Baker Street and Waterloo Railway (Bakerloo), the Charing Cross, Euston and Hampstead Railway (Hampstead) and the Great Northern, Piccadilly and Brompton Railway, (Piccadilly), which all opened between 1906 and 1907. When the "Bakerloo" was so named in July 1906, The Railway Magazine called it an undignified "gutter title". By 1907 the District and Metropolitan Railways had electrified the underground sections of their lines.
In January 1913, the UERL acquired the Central London Railway and the City & South London Railway, as well as many of London's bus and tram operators. Only the Metropolitan Railway, along with its subsidiaries the Great Northern & City Railway and the East London Railway, and the Waterloo & City Railway, by then owned by the main line London and South Western Railway, remained outside the Underground Group's control.
A joint marketing agreement between most of the companies in the early years of the 20th century included maps, joint publicity, through ticketing and UNDERGROUND signs, incorporating the first bullseye symbol, outside stations in Central London. At the time, the term Underground was selected from three other proposed names; "Tube" and "Electric" were both officially rejected. The term Tube was later adopted alongside the Underground. The Bakerloo line was extended north to Queen's Park to join a new electric line from Euston to Watford, but the First World War delayed construction and trains reached Watford Junction in 1917. During air raids in 1915 people used the tube stations as shelters. An extension of the Central line west to Ealing was also delayed by the war and was completed in 1920. After the war, government-backed financial guarantees were used to expand the network and the tunnels of the City and South London and Hampstead railways were linked at Euston and Kennington; the combined service was not named the Northern line until later. The Metropolitan promoted housing estates near the railway with the "Metro-land" brand and nine housing estates were built near stations on the line. Electrification was extended north from Harrow to Rickmansworth, and branches opened from Rickmansworth to Watford in 1925 and from Wembley Park to Stanmore in 1932. The Piccadilly line was extended north to Cockfosters and took over District line branches to Harrow (later Uxbridge) and Hounslow.