The expectations of official control are high, and resources are limited. What is most important in conducting such control? How can we prioritise between risks which are not directly comparable? Which approach provides most safety, relative to resource allocation? Risk categorisation is a tool to make such assessments more explicit, fact-based and transparent. The quality of risk management can never be better than the available knowledge of the risks. Prioritisation of official control must be based on knowledge available at any given time, and not on the basis of knowledge that is being worked towards obtaining in the future. The report presents a new model that incorporates the following knowledge types into a system, with a view to improving resource use in official control.- Knowledge of the life-cycles of products, processes and services, - Knowledge of the products, processes and services of different industries, - Knowledge of the individual traders. The model has been developed for prioritising control of the various risks in the food chain, but could also be suitable, and used for, prioritising of control of other risk types.