In this paper we present an approach to sharing a user model among several adaptive hypermedia applications. Current adaptive hypermedia applications often realize the user model as the internal part of the system without any possibility to share this model with other applications. We introduce a web service called UMOWS (User Model Web Service). The web service acts as a store of user characteristics represented in pre-defined ontologies that define semantics of the stored knowledge. Access and corresponding privileges to the web service is managed by the user through the management interface. The user is also allowed to inspect/modify the state of the user model.