The Hammersmith & City line is a London Underground line that runs between Hammersmith in west London and Barking in east London. Coloured pink on the Tube map, it serves 29 stations over 15.8 miles (25.5 km). Between Farringdon and Aldgate East it skirts the City of London, the capital's financial heart, hence the line's name. Its tunnels are just below the surface and are a similar size to those on British main lines. Most of the track and all stations are shared with the District, Circle or Metropolitan lines. Over 141 million passenger journeys are made each year on the Hammersmith & City and Circle lines.

The London Underground is a rapid transit system serving Greater London and some parts of the adjacent home counties of Buckinghamshire, Essex and Hertfordshire in England.