This paper gives details of this NDBS project, which is 'mapping' the entire non-domestic building stock of England and Wales - some 2 million premises. The project draws on detailed surveys of thousands of buildings and data from numerous other sources. The result of this research is a database from which it is possible to draw inferences from the local survey data and apply them to the national stock. As its first major output, the database has been used to estimate the national floor area and the exposed wall, glazing and roof areas. The database enables analysts to follow trends in the composition of the non-domestic stock, and its fuel and energy use. It has been used to predict the probable outcomes of various energy-efficiency measures and to monitor the effectiveness of such measures once implemented.