The quality of the built environment depends critically on the concept of sustainability and, in particular, on designs which are energy efficient and environmentally friendly. This paper gives an account of the successful application of computer-based simulations of the physical environment made available to architects through an Energy Design Advisory Service and used parametrically within a research project carried out jointly with a design and build company. It goes on to indicate how emerging multimedia technology can be used to provide an explanation, particularly to those who are technically unsophisticated, of the complexity of the way in which design decisions impact upon the energy efficiency and environmental friendliness of buildings.