Which London Underground line serves Heathrow Terminal 5?

The Piccadilly line serves Heathrow Terminal 5.

The line connects Heathrow Airport with central and north-west London, running through major destinations such as Hammersmith, South Kensington, Leicester Square, and King’s Cross St Pancras. Heathrow Terminal 5 is served by the western branch of the line, which also serves Heathrow Terminals 2 & 3 and Terminal 4.

The Piccadilly line began serving Heathrow Airport in 1975, when the extension to Heathrow Central opened. The Terminal 4 station opened in 1986, and Terminal 5 station opened in 2008 alongside the airport terminal.

The Elizabeth line also serves Heathrow, but it is not a London Underground line. That distinction matters because the question asks specifically about the Tube. Heathrow’s airport stations therefore have services from both London Underground and National Rail-style urban rail systems, depending on the terminal.