Abstract: The idea of a green belt around London emerged in the 19th century in response to the health-wise catastrophic conditions of that period. At a time when cholera was believed to be airborne, providing fresh air for the city became a question of public heath, made urgent by such disasters as the cholera outbreak in Soho in 1853-54. Communal parks and green girdles or belts were installed as a policy response to such emergencies, to serve as the "green lungs" for the city. In recent years, the Green Belt has been foregrounded in the effort to promote environmentally friendly sustainable development; the last two mayors of London have both declared further protection and extension of London's Green Belt. This paper examines how the narrative and functionality of London's Green Belt has evolved since its conception as an urban public health strategy. Today, health issues are no longer the primary argument for preserving the Green Belt. A close analysis of the actual uses and spaces of the Green Belt reveals that, contrary to the image its name might conjure—that of open, vegetated parks—the Belt is actually a variegated landscape of varying degrees of urbanization, serving the modern city of London with such vital infrastructure as highways and airports. The paper concludes with suggestions on how the narrative and management of the London Green Belt could be adapted to contemporary ideas for environmental and social sustainability, including promoting health and livability for Londoners.