The paper surveys the current status of the models for representing, manipulating and analyzing dimensioning and tolerancing data behind the major computer-aided tolerancing (CAT) systems, now commercially available. The solid models and tolerance models that these systems adopt, and their implications for the successful integration of CAT and CAD/CAM are discussed. There are two main purposes. First, the attention is focused on the theoretical backgrounds of every CAT system analyzed, for understanding its limits and its usefulness in design and manufacturing practice. The other purpose is to present a comparison among these systems to support the designer and the manufacturing engineer, as well as the researchers, in the choice of the system will be more proper to everyone. Finally, the research work that remains to be carried out, to improve the future CAT systems and their integration with CAD/CAM is sketched out
