Virtual Documents are a user interaction medium for knowledge systems that exploits the (then) new capabilities of the Web for dynamic hypermedia and the AI techniques for model-based generation of natural language explanations. In contrast to convention GUIs, the virtual document dynamically generates its content as a dialog with the reader. The content is full of hyperlinks, which the user follows to follow up with questions or move to the next level of detail. Tom wasn’t the first to show a dynamic web site, but he was a vocal proponent of the use of generative dynamic interfaces as a communication medium.