Users who work together require adequate information about their cooperative environment: about other group members presence and activities, about shared artefacts, etc. In the CSCW literature several concepts, prototypes, and systems for providing this group awareness information have been presented. In general, they capture information from the environment, process it, and present it to the users. This paper addresses the processing aspect; in particular, we present a concept for processing awareness information by means of awareness contexts. With this concept we address the problem of contextualising event notifications enabling the presentation of notifications in the appropriate user situation. We describe a lightweight model and its integration into an event and notification infrastructure. We report on an empirical study, and draw some conclusions for the design of context-awareness for cooperative environments.