Abstract. Process–aware information systems (PAIS) must provide sufficient flexibility to their users to support a broad spectrum of application scenarios. As a response to this need adaptive process management systems (PMS) have emerged, supporting both ad-hoc deviations from the predefined process schema and the quick adaptation of the PAIS to business process changes. This newly gained runtime flexibility, however, imposes challenging security issues as the PMS becomes more vulnerable to misuse. Process changes must be restricted to authorized users, but without nullifying the advantages of a flexible system by handling authorizations in a too rigid way. This paper discusses requirements relevant in this context and proposes a comprehensive access control (AC) model with special focus on adaptive PMS. On the one hand, our approach allows the compact definition of user dependent access rights restricting process changes to authorized users only. On the other hand, the defini...