When properly designed, a microbiological risk assessment (MRA) is an objective and systematic evaluation of existing scientific knowledge to help risk managers making an informed decision about how to handle food safety issues. Together with epidemiological based information and economic analysis it can provide the best information for control measures. One of these control measures concerns setting food safety criteria. In this document some historical backgrounds are presented how food safety management has been evaluated in course of time from mythology, via prohibition and precautionary principles to a science based approach. MRA-tools are described and examples of risk assessment approaches are presented as a basis for setting microbiological criteria.