CAE Emmersion is based on the CAE GESI constructive simulation system used extensively by armies for command and staff training. It provides an environment for emergency managers to plan, test, and train their response strategies in a safe and controlled environment. Decision makers need to anticipate the potential consequences of a crisis situation and to use available resources effectively to bring the situation under control while protecting the public and limiting damages in the best possible way. More than ever before, government agencies, local authorities and corporations managing critical infrastructures must be ready to face today’s threats and risks to protect population and assets. The best measure to be prepared for crisis situations are emergency plans that answer the question "what if" and are supported by a team of well-trained crisis and emergency managers. CAE's Emmersion simulation environment is an essential aid to meet these challenges. It simulates comprehensive emergency situations, providing a constructive simulation environment to develop emergency plans, and then train and prepare emergency managers to face crisis situations.