Recent developments in display technology, specifically head-mounted displays slaved to the user’s head position, techniques to spatialize sound, and computer-generated tactile and kinesthetic feedback allow humans to experience impressive visual, auditory, and tactile simulations of virtual environments. However, while technological advancements in the equipment to produce virtual environments have been quite impressive, what is currently lacking is a conceptual and analytical framework in which to guide research in this developing area. What is also lacking is a set of metrics which can be used to measure performance within virtual environments and to quantify the level of presence experienced by participants of virtual worlds. Given the importance of achieving presence in virtual environments, it is interesting to note that we currently have no theory of presence, let alone a theory of virtual presence (feeling like you are present in the environment generated by the computer) or telepresence (feeling like you are actually “there” at the remote site of operation). This in spite of the fact that students of literature, the graphic arts, the theater arts, film, and TV have long been concerned with the observer’s sense of presence. In fact, one might ask, what do the new technological interfaces in the virtual environment domain add, and how do they affect this sense, beyond the ways in which our imaginations (mental models) have been stimulated by authors and artists for centuries? Not only is it necessary to develop a theory of presence for virtual environments, it is also necessary to develop a basic research program to investigate the relationship between presence and performance using virtual environments. To develop a basic research program focusing on presence, several important questions need to be addressed. The first question to pose is, how do we measure the level of presence experienced by an operator within a virtual environment? We need to develop an operational, reliable, useful, and robust measure of presence in order to evaluate various techniques used to produce virtual environments. Second, we need to determine when, and under what conditions, presence can be a benefit or a detriment to performance.