This chapter will deal with the issue of interaction in complex virtual environments (VEs) for virtual prototyping (VP). First, we will review briefly the novel I/O devices currently being used in VR, and classify VEs with respect to the real environment being simulated. Then, several interaction techniques will be discussed, both for VEs in general and for VP in particular. The last two sections give a more technical view on the issue of how to describe VEs and on the overall architecture of VR systems.
