A new automotive active safely system, the Vehicle Dynamics Control System (VDC) of BOSCH was introduced on the market in 1995. Besides improving the ABS/ASR functions, VDC will also actively support the driver in critical situations of lateral vehicle dynamics. This system includes new ABS/ASR-control algorithms and a superimposed control algorithm, the vehicle dynamics controller. Furthermore, an extension of the standard ABS/ASR-hydraulic system was necessary as well as the development of new automotive sensors. During all phases of the interdisciplinary system development, tests on experimental cars and extensive computer simulations were used in parallel.In order to provide adequate simulation models for different tasks, a modular concept for the simulation tool is important. Furthermore, a transparent and portable application of the control algorithm for both, experiment and simulation, is required. Therefore FASIM (FAhrdynamik-SIMulation) a modular simulation package for non-linear vehicle dynamics is used. The vehicle is decomposed into subsystems of different type and complexity with definite interfaces. The subsystems are included in a module library and can be linked to build up a complete vehicle model. The features of FASIM will be briefly outlined in this paper. The main emphasis will be put on describing the use of simulation tools during the different stages of the development of VDC. During the validation process, the quality of the vehicle model is studied first. Considering the validated model, the performance and robustness of the controller w.r.t. modifications of vehicle parameters can be studied. Furthermore it is shown how the simulation was used for the specification of VDC-components like sensors and hydraulic unit and for the verification and quality assurance of the controller software. The controller safety concept was tested by simulating sensor signal faults. Finally, the potential of VDC is demonstrated by simulating driving maneuvers. In the future, further applications of FASIM will be possible by using a real-time simulation system for hardware in the loop simulation.