The position invariant geometric inaccuracies of a machine tool are the ®rst to in¯uence the quality of machined parts. A systematic approach is presented to identify some of these errors on a ®ve-axis machine tool. The methodology is applied to the link error parameters such as joint misalignments, angular o set and rotary axis separation distance. A method based on the mathematical analysis of singularities of linear systems is used to assist in selecting a minimal but su cient set of link error parameters for the calibration of a machine tool. A number of criteria are proposed in order to verify that the identi®ed parameters accurately predict the positioning errors of the true machine. Finally, the numerical e ectiveness of this method is shown through simulations.