Current Computer-Aided Architectural Design (CAAD) tools facilitate representation, visualization and simulation of the structure, the spaces and the furnishings of the built environment, but do not facilitate visualization and dynamic simulation of the people who use it. In fact, heretofore it has been practically impossible to represent and simulate the physical, social, psychological, and cultural interactions between the designed environment and its intended occupants. We are developing a visualization and evaluation tool which will allow designers to observe the use of the spaces they design by inserting in them animated human figures, which we call SVUs (Smart Virtual Users). Such computer animated human figures will make it possible to visualize the designed spaces "in use," and to observe directly the physical and social dynamics of the interaction between the building and its intended occupants. By ascribing to the SVUs different human characteristics and capabilities, they could simulate the behavior in space of different populations, including handicapped users, users representing different age groups and different genders. SVUs are intended to be a tool in which Environmental Design, Computer Science, and Social Science converge for the creation of computer aided design assistants for architects and urban designers.