The Charing Cross, Euston and Hampstead Railway (CCE&HR), also known as the Hampstead Tube, was a railway company established in 1891 that constructed a deep-level underground "tube" railway in London. Construction of the CCE&HR was delayed for more than a decade while funding was sought. In 1900 it became a subsidiary of the Underground Electric Railways Company of London (UERL), controlled by American financier Charles Yerkes. The UERL quickly raised the funds, mainly from foreign investors. Various routes were planned, but a number of these were rejected by Parliament. Plans for tunnels under Hampstead Heath were authorised, despite opposition by many local residents who believed they would damage the ecology of the Heath.

When opened in 1907, the CCE&HR's line served 16 stations and ran for 7.67 miles (12.34 km) in a pair of tunnels between its southern terminus at Charing Cross and its two northern termini at Archway and Golders Green. Extensions in 1914 and the mid-1920s took the railway to Edgware and under the River Thames to Kennington, serving 23 stations over a distance of 14.19 miles (22.84 km). In the 1920s the route was connected to another of London's deep-level tube railways, the City and South London Railway (C&SLR), and services on the two lines were merged into a single London Underground line, eventually called the Northern line.

Within the first year of opening, it became apparent to the management and investors that the estimated passenger numbers for the CCE&HR and the other UERL lines had been over-optimistic. Despite improved integration and cooperation with the other tube railways, and the later extensions, the CCE&HR struggled financially. In 1933 the CCE&HR and the rest of the UERL were taken into public ownership. Today, the CCE&HR's tunnels and stations form the Northern line's Charing Cross branch from Kennington to Camden Town, the Edgware branch from Camden Town to Edgware, and the High Barnet branch from Camden Town to Archway.

The London Underground (also known simply as the Underground, or by its nickname the Tube) is a rapid transit system serving Greater London and some parts of the adjacent counties of Buckinghamshire, Essex and Hertfordshire in the United Kingdom.The Underground has its origins in the Metropolitan Railway, the world's first underground passenger railway. Opened on 10 January 1863, it is now part of the Circle, District, Hammersmith & City and Metropolitan lines. The first line to operate underground electric traction trains, the City & South London Railway in 1890, is now part of the Northern line. The network has expanded to 11 lines, and in 2020/21 was used for 296 million passenger journeys, making it the world's 12th busiest metro system. The 11 lines collectively handle up to 5 million passenger journeys a day and serve 272 stations.The system's first tunnels were built just below the ground, using the cut-and-cover method; later, smaller, roughly circular tunnels—which gave rise to its nickname, the Tube—were dug through at a deeper level. The system serves 272 stations and has 250 miles (400 km) of track. Despite its name, only 45% of the system is under the ground: much of the network in the outer environs of London is on the surface. In addition, the Underground does not cover most southern parts of Greater London, and there are only 33 stations south of the River Thames.The early tube lines, originally owned by several private companies, were brought together under the "UndergrounD" brand in the early 20th century, and eventually merged along with the sub-surface lines and bus services in 1933 to form London Transport under the control of the London Passenger Transport Board (LPTB). The current operator, London Underground Limited (LUL), is a wholly owned subsidiary of Transport for London (TfL), the statutory corporation responsible for the transport network in London. As of 2015, 92% of operational expenditure is covered by passenger fares. The Travelcard ticket was introduced in 1983 and Oyster card, a contactless ticketing system, in 2003. Contactless bank card payments were introduced in 2014, the first public transport system in the world to do so.The LPTB commissioned many new station buildings, posters and public artworks in a modernist style. The schematic Tube map, designed by Harry Beck in 1931, was voted a national design icon in 2006 and now includes other TfL transport systems such as the Docklands Light Railway, London Overground, TfL Rail, and Tramlink. Other famous London Underground branding includes the roundel and the Johnston typeface, created by Edward Johnston in 1916.