Prioritization of document, such as email messages, is disclosed. In one embodiment, a computer-implemented method first receives a document. The method generates a priority of the document, based on a document classifier such as a Bayesian classifier or a support-vector machine classifier. The method then outputs the priority. In one embodiment, the method includes alerting the user based on an expected loss of now-review of the document as compared to an expected cost of alerting the user of the document, at a current time. Several methods are reviewed for display and interaction that leverage the assignment of priorities to documents, including a means for guiding visual and auditory actions by priority of incoming messages. Other aspects of the machinery include a special viewer that allows users to scope a list of email sorted by priority so that it can include varying histories of time, to annotate a list of messages with color or icons based on the automatically assigned priority, to harness the priority to control the level of detail provided in a summarization of a document, and to use a priority threshold to invoke an interaction context that lasts for some period of time that can be dictated by the priority of the incoming message.