The Current Computer-Aided Design (CAD) and Knowledge-Based Systems (KBS, expert systems) tools are changing mechanical engineering design. Future development and integration of these technologies is dependent on an understanding of the methodology of the mechanical design process, an area of little study and one that is poorly understood. This paper reports on the progress of an effort to understand how practicing engineers perform design. The approach is to record engineers' verbalization of their solution of carefully constructed design problems. The recordings are reduced to determine the intellectual tasks and problem-solving methods used. The results will determine what needed capabilities future intelligent CAD systems will need to aid design engineers.