The context in which designers operate is becoming more and more complex, owing to the large number of codes, new materials, technologies and professional figures, new instruments are needed, therefore, to support and verify design activity. The results obtained in the first years of'computer era'were barely sufficient. The hardware and software available today is capable of producing a new generation of CAD systems which can aid the designer in the process of conceiving and defining building objects. At the CAD Laboratory in the Department of Building and Environmental Control Techniques at the'La Sapienza'University of Rome, research is being carried out with the aim of defining a new kind of Knowledge-based assistant for architectural design. To this purpose a partnership has been established whit a private firm called CARTESIANA, whose partners are software houses, designing and building associations.