First comprehensive concepts for online teaching via computer networks were developed at the FernUniversität Hagen, the only distance teaching institution at university level in Germany, nearly three years ago. In the meantime an extensive prototype of the Virtual University has been implemented and tested in practice with over a thousand students. Different kinds of course materials are offered to the students: multimedia courses, videos, computer based training, highly interactive courses with integrated working and experimental environment, animations and pure text. In this paper communication systems and scenarios are presented and analysed as to their didactical use and feasibility in practice. For example ProShare, NetMeeting, and MBone are used for video communication between students and lecturer. Students participate in seminars as if they were attending in person, but save the time and travel expense that would be necessary if they attended in person.