The expansion of Heathrow Airport is a series of proposals to add to the runways at London's busiest airport beyond its two long runways which are intensively used to serve four terminals and a large cargo operation. The plans are those presented by Heathrow Airport Holdings and an independent proposal by Heathrow Hub with the main object of increasing capacity.

Heathrow Airport, called London Airport until 1966, is the main international airport serving London, the capital of England and the United Kingdom. It is the largest of the six international airports in the London airport system. The airport is owned and operated by Heathrow Airport Holdings, owned mostly by Qatar Investment Authority, Public Investment Fund and CDPQ. In 2023, Heathrow was the busiest airport in Europe, the fourth-busiest airport in the world by passenger traffic and the second-busiest airport in the world by international passenger traffic. As of 2023, Heathrow is the airport with the most international connections in the world.