Virtual Reality (VR) is usually described as a collection of technological hardware: a computer capable of 3D real-time animation, a head-mounted display, data gloves equipped with one or more position trackers. However, this focus on technology is disappointing for clinicians interested in developing virtual environments to be used in assessment and therapy. To overcome this limitation this chapter describes VR as an advanced communication tool: a communication medium in the case of multi-user VR and a communication interface in single-user VR. Two are the core characteristics of VR as communication tool: the perceptual illusion of nonmediation and the sense of community. The first characteristic of a satisfying virtual environment is the disappearance of mediation, a level of experience where both the VR system and the physical environment disappear from the user's phenomenal awareness. The second characteristic is the sense of community developed by interaction. Through interaction made possible by multi-user VR, individuals find or form groups that share interests. So, information exchange becomes the carrier for expressing self-concept and eliciting emotional support. Within this view, experiencing presence and telepresence does not depend so much on the faithfulness of the reproduction of 'physical' aspects of 'external reality'--which is also a social production, and not a primitive or 'natural' fact--as on the capacity of simulation to produce a context in which social actors may communicate and cooperate. The consequences of this approach for the design and the development of clinical oriented VR systems are presented, together with the methodological and technical implications for the study of advanced human-computer interaction.