An important characteristic of most computer supported work environments is the distribution of work over individuals or teams in different locations. This leads to what we nowadays call `virtual' environments. In these environments communication between actors is to a large degree mediated, i.e. established through communications media (telephone, fax, computer networks) rather in a face-to-face way. Unfortunately, mediated communication limits the effectiveness of knowledge exchange in virtual environments because the communications media employed are less suited for tacit knowledge than for explicit, codified knowledge.