The method of computer-simulation is still a young field, but especially useful for the investigation of complex systems typical for topics of environmental psychology. This paper offers a brief overview of the method, especially its field of application, the procedure of developing simulation models and ideas for using them for solving practical tasks of environmental psychologists. The method is especially useful for handling problems, where the system of interest can not be reduced to a few simple parts with a few simple interactions. Additionally, the method is ideal for investigating and forecasting dynamic developments over time. When using simulation models for planning and guiding campaigns, which aim at influencing social developments, it is crucial not to assign their results directly to reality. Simulation-results must be concretized to plans, which also consider aspects that were not included in the abstract formal model. Further, the simulation models must be adapted continuously to information about the influenced system that becomes available during the realization of the campaign.