For use in future versions of the integrative reports called Milieubalans ('environmental balance') and Milieuverkenning ('environmental outlook') RIVM has chosen to present an overview of environmental issues, especially those related to actual and future environmental policies in the Netherlands, in terms of so called target and related steering variables. This definition report describes the elaboration of this approach when it is applied to the complete area of interest 'radiation'. Together with other definition reports it is supposed to be the justification of choices which are made in defining the sequence of subjects and the minimum set of variables in the future versions of the Milieubalans and the Milieuverkenning. The elaboration is guided by the policy document 'Radiation protection and risk management' (Omgaan met risico's van straling). The policy can be characterized as 'risk management by focusing directly on the sources of radiation'. In other words steering at the beginning and setting limits at the end of the source-risk-chain. Therefore, in this report it is concluded that the complete source-risk-chain has to be analyzed and modelled. The area of interest 'radiation' is divided into areas corresponding to the source categories which are used in the policy document. For each area possible target and steering variables, together with related target and reference values, are collected. Determination of the present (diagnosis) and future (prognosis) values of the target variables is also investigated. In conclusion an indication is given of the activities, which are advisable for the coming years in order to make the target variables operational. The next phases are roughly outlined.