Parallel machines represent a new generation of machine tool. Through reducing the number of setups both the efficiency and the accuracy of the machining process is increased within the part domain. While Flexible Manufacturing Systems (FMSs) and Machining Cells (MCs) are said to be agile, the parallel machine is the first stand-alone machine which can claim to have this property. This makes them ideally suited for machining small batch sizes and for rapid prototyping. Unfortunately like FMSs and MCs these machines will be largely underutilized if agile data generation, processing and transfer mechanisms are not incorporated into CAD/CAM systems. One major hurdle to achieving this objective is the development of an automatic process planning system for parallel machines. This presents new challenges beyond those encountered in process planning for sequential machining. In this paper we discuss two aspects of parallel machines which impact on process planning. These are (1) the part domain for parallel machines and (2) the machine configuration.