The Web represents an information space where the amount of information grows exponentially. This calls for personalized interaction between users and web-based information systems providing information. Current systems provide a certain level of personalization, which allows the user to set up her preferences manually. Improved efficiency of information acquisition can be achieved by personalization based on a user’s particularities used for the adaptation of content or navigation in the information space. A user model that reflects a real user, who requires information provided by an information system, is required for successful personalization. We present an ontology-based approach to user modeling and describe the user model that we designed for a web-based information system aimed at job acquisition. We point out several advantages of the ontology-based approach, namely the sharing of the ontology with other applications and reusability.