In the chemical industry the development of new processes and the revision of operating processes are the main tasks of chemical engineering divisions. After defining the idea of process development and process revision the fundamentals in dealing with complete chemical processes like experiment, modelling and full-scale operation if possible will be explained in this paper. The meaningfulness and the limits of these elements will be shown and hints are given for available and useful tools and instruments. Furthermore evaluating tools as well as siting problems and other practical aspects are considered.