The simulation and overall testing of AD (Autonomous Driving) and ADAS (Advanced Driver-Assistance Systems) systems is probably one of the most complex tasks today. We cannot talk about a specific class of simulation in this case, it is about the management of many parallel simulations describing the behaviour of a highly complex autonomous or ADAS-equipped vehicle. Even the nuances can be considered in the models; the aerodynamics, the suspension and powertrain system, the electronic subsystems and the ADAS sensors as well as the AI-based perception and control systems. This is all embedded in a virtual environment where the road, the weather, visual conditions, pedestrians and similar vehicles are modelled and simulated. It sounds like a very difficult environment to simulate! So why do all the OEMs bother? There is a good reason; it is impossible to effectively validate AD and ADAS systems without simulation.