The aim of this paper is to present in some detail a CAT model consistent with the more recent concepts issued from the ISO/TC 213 work, in the frame of the well-known ISO GPS Project [ISO/TC 213 Business Plan, 2001-07-02, pp. 1–3], as well as its related theoretic foundations. The presented model is not only a theoretical methodology, because it has been successfully implemented in CATIA ® software, enabling analysis and manipulations of tolerance zones as well as assembly simulations.