Th e Problem. Th e consequences and implications of simulator sickness for the validity of simulation can be severe if not controlled and taken into account (Casali, 1986). Many of today's driving simulators are used to perform research, training, or proof of design activities. A prerequisite to generalizing the results found in research conducted in a simulator is an understanding of the validity of the resulting experience. Without question, simulator sickness is a factor that can aff ect the validity of research simulators. Given the potential consequences of simulator sickness, it is diffi cult to assess the value of the results obtained from a simulator study known to have signifi cant sickness problems. Role of Driving Simulators. Th ere are alternatives to driving simulators for studying most, if not all, issues. However, these alternatives are oft en unsafe, do not provide a well-controlled environment, and require large sums of money to implement. Th us, driving simulators are necessary and the associated issues of simulator sickness need to be addressed. Key Results of Driving Simulator Studies. Simulator sickness can aff ect a driver's performance in a variety of negative ways due to inappropriate behaviors, loss of motivation, avoidance of tasks that are found disturbing, distraction from normal attention allocation processes, and a preoccupation with the fact that something is not quite right. On the positive side, simulator selection, participant screening, scenario design, and control of the environment can all reduce the incidence of simulator sickness. Scenarios and Dependent Variables. Examples of the sorts of scenarios that lead to extremes of simulator sickness are discussed. Additionally, the various measures that have been used against simulator sickness are highlighted, including some with predictive validity. Platform Specifi city and Equipment Limitations. Simulator sickness appears to be most extreme in fully immersive environments and when head-mounted displays are used. A motion base does not necessarily reduce simulator sickness symptoms.