A green belt is an area of land that usually surrounds a town or city, and is kept open by government restrictions on further development. Often it comprises both public and private land.

Green belts provide both recreational areas and landscape, but their main purpose is to contain cities, diverting future growth, and preventing cities and towns from merging.

It grew out of Sir Ebenezer Howard's "Garden City" approach to town planning, which aimed to provide natural areas for residents of cities. Garden cities were surrounded by countryside; city expansion was only to take place by developing new garden cities on the other side of the green belt. The result would be clusters of cities grouped around a central city. Several garden cities (e.g., Welwyn in England) were built in Britain.

In the 1920s, London's government called for study of an "agricultural belt...