With the ICRP recommendations Publications 103, 109 and 111 (ICRP, 2007; ICRP 2009a, 2009b), new concepts and quantities have been introduced into emergency management and rehabilitation. Two of them will possibly influence national procedures, but for sure they will influence countermeasure simulation approaches: 1. The concept of a “reference level” for emergency and existing controllable exposure situations that represents the level of dose or risk, above which it is judged to be inappropriate to plan to allow exposures to occur, and for which therefore protective actions should be planned in advance. 2. When deciding on the optimum course of protective actions, all exposure pathways and all relevant actions have to be taken into account. The major changes for the simulation models result from the second recommendation that all exposure pathways must be considered when deciding on protective actions. So far all countermeasure simulations in the early phase of an emergency are carried out by considering individual countermeasures such as sheltering or evacuation, if some dose limit for the respective action is exceeded. This approach has to be changed and strategies of several countermeasures analysed and simulated with the ultimate goal not to exceed the reference level over a given time period, typically one year.