The evolution of mobile technologies, like web-enable cellphones, PDAs and wireless networks, makes it now possible to use these technologies for collaborative work through web-based groupware systems. However, due to the limitations of these technologies, some adaptation is essential in these systems. In order to adapt their behaviour to the user's context, groupware systems must be built as context-aware systems. Besides the characteristics of the user's context, we believe that the user's preferences should also be taken into account by the adaptation process. In this paper, we present a two-fold approach for adapting the informational content delivered to a mobile user by web-based groupware systems: we propose a filtering mechanism which considers both the current context and preferences for this context. The notion of context is represented through an object-based model we have proposed, which takes into account the user's physical context as well as the user's collaborative context, including elements dedicated to the collaborative process in which the user is involved (notions of group, role, activity, etc.). The user's preferences are represented by a set of pre-defined profiles, which are exploited by the adaptation process in order to organize the delivered information into several levels of detail, based on a progressive access model. The proposed filtering mechanism is performed in two steps: first, it analyses the user's current context and selects, among the user's pre-defined profiles, those which have been defined for a situation found in this context. Second, it uses the progressive access model in order to filter and organize the available information, according to the selected profiles.