Computer Aided Process Planning (CAPP) has been recognized as playing a key role in Computer Integrated Manufacturing (CIM). In the last two decades, a tremendous effort has been made in developing CAPP systems. However, the benefits of CAPP in the real industrial environment are still to be seen. In this paper, a comprehensive summary on the state-of-the-art and projection of future trends in CAPP is presented to help make decisions concerning CAPP implementation today and to aid in guiding research for tomorrow. We systematically overview the historical background of the development of CAPP and discuss the current techniques which includes the implementation approaches, GT technology, application of AI techniques, programming languages, etc., for implementation CAPP systems. About 14 well-known CAPP systems, which are based on the variant, generative or semi-generative approach, are briefly introduced in this paper. In total about 156 currently existing CAPP systems are listed in Table 1 in the appendix. Table 1 provides the general information of the existing systems, such as the characteristics of the systems, the domain of planable workpieces, implementation approaches, commercial situation, interfacing abilities, programming languages, references, and developers, etc. Future trends proposed in this paper covers the topics about interfacing, integration, AI techniques, and single data base systems, as well as PC, workstations and software migration strategy, etc., which might be used to guide coming research. More than 200 technical papers have been read and are referenced at the end of this paper.