The Twentieth Century Society (C20) is a British charity which campaigns for the preservation of architectural heritage from 1914 onwards. The society's interests embrace buildings and artefacts that characterise 20th-century Britain. It is formally recognised as one of the National Amenity Societies, and as such is a statutory consultee on alterations to listed buildings within its period of interest, and must be notified of any proposed work to a listed building which involves any element of demolition.