The London Underground network comprises 11 lines.
These lines are Bakerloo, Central, Circle, District, Hammersmith & City, Jubilee, Metropolitan, Northern, Piccadilly, Victoria and Waterloo & City. They operate as one integrated rapid-transit system, although their histories, routes and train designs differ substantially.
The figure of 11 refers specifically to London Underground lines. It does not include other services shown on the wider London rail map, such as the London Overground, Elizabeth line, Docklands Light Railway or Tramlink. This distinction is a common source of confusion because the Underground map displays several non-Underground railways.
The network developed from separate railway companies and routes. The Metropolitan Railway opened in 1863, while deep-level electric lines appeared later. Some modern lines, including the Victoria and Jubilee lines, were purpose-built in the twentieth century, whereas others evolved from nineteenth-century railways.