This paper presents a method to determine set-ups for mechanical workpieces. The method specifies the minimal number of set-ups needed to machine the workpiece, the machine to be used for each set-up, the orientation of the workpiece with respect to the machine in each set-up, the operations to be executed in each set-up and the precedence relations between the set-ups. A kind of feature-based workpiece description is used. The method determines all the possible solutions with the minimal number of set-ups, taking into account tolerance and precedence relations between the elements (features). The program GEOPS is the implementation of the method and was used to evaluate the method. The use of the program uncovered some necessary extensions and enhancements to the system.