Abstract. As the use of computers and data communication technologies spreads, network security systems are becoming increasingly complex, due to the incorporation of a variety of mechanisms necessary to fulfil the protection requirements of the upcoming scenarios. The integrated design and management of different security technologies and mechanisms are thus of great interest. Especially in large-scale environments, the employment of security services and the design of their configurations shall be supported by a structured technique which separates the consideration of the system as a whole from the detailed design of subsystems. To accomplish this goal, this paper presents a scalable approach for the modelling of large security systems, relying on the concepts of policy-based management and model-based management.