In the research project EPOS1 we build a pro-active, contextsensitive support system to aid the user with his knowledge work, which is mostly about searching, reading, creating, and archiving of documents. In order to avoid distracting the user, the context gathering is realized by installable user observation plugins for standard applications such as Mozilla Firefox and Thunderbird. The main part of this paper is about the definition of a context model for the personal knowledge management domain. The context model incorporates only contextual elements relevant to satisfy the knowledge worker’s potential information need. It stores only information items known to the user (such as links to his own documents, folders, etc.), as well as, shared ontologies to assure an understanding of the context. The context is modeled in RDF/S and can be retrieved by contextaware applications from the context support system via an XML-RPC call.