Information about the user's environment offers new opportunities and exposes new challenges in terms of time-aware, location-aware, device-aware and personalized applications. Such applications constantly need to monitor the environment - called context - to allow the application to react accordingly to this context. Context-awareness is especially interesting in mobile scenarios where the context of the application is highly dynamic and allows the application to deal with the constraints of mobile devices in terms of presentation and interaction abilities and communication restrictions. Current context-aware applications often realize sensing of context information in an ad hoc manner. The application programmer needs to deal with the supply of the context information including the sensing of the environment, its interpretation and its disposal for further processing in addition to the primary purpose of the application. The close interweavement of device specific context handling with the application obstructs its reuse with other hardware configurations. Recently, architectures providing support for context-aware applications have been developed. Up to now such architectures are not trimmed to the special requirements of mobile devices regarding particularly the limitations of network connections, limited computing power and the characteristics of mobile users. This paper proposes an architecture and a software framework - the hydrogen context framework -which support context-awareness for considering these constraints. It is extensible to consider all kind of context information and comprises a layered architecture. To prove the feasibility the framework has been implemented to run on mobile devices. A context-aware postbox is realized to demonstrate the capabilities of the framework.