Virtual Reality is a subject of rising importance since it is representative of the expanding interface between human beings and computers. Kim Jounghyun is an associate professor in computer science and engineering at Pohang University of Science and Technology (POSTECH). He has contributed the following article on virtual reality, the first of what will be a series of eight on the topic. Virtual Reality (VR) is the creation of a synthetic experience via a user-oriented system. The experience is ynthetic, llusory or irtual because the sensory stimulation to, and interaction by the user of the system is simulated and made possible by a computer and associated sensors (e.g. motion tracking, voice recognizer, etc.) and displays (head worn displays, 3D sound systems, etc.) The figure below captures the basic architecture of a typical VR system. In the figure, the user is depicted as driving in a virtual world, one that is displayed to him visually, aurally and kinesthetically (force feedback) through the head-mounted display, the earphone, and the handle/pedal interface. The displays are generated and controlled by the computer program. The computer program also accepts user input/action (e.g. head movements by the user) through sensors and processes them to be reflected to the virtual environment and back to the displays. Of what value is a virtual experience Obviously, it allows people to gain experience of things that would otherwise be very difficult or even impossible to attain in real life, such as going to the South Pole or to the Moon. The virtual experience can even be something imaginary and abstract (rather than real life inspired), like experiencing an abstract mathematical world or a world envisioned by an artist (e.g., Alice in the Wonderland). Such virtual experiences are useful for many purposes including training, education, and entertainment. In addition, the underlying and enabling technologies of VR can be applied to many other areas, rather than just creating virtual experiences. For instance, VR can be viewed as an advanced form of human computer interaction (HCI), new enriched communication medium, or intuitive information visualization method. It is noteworthy that innovations in the area of human computer interaction have been one of the important factors in proliferating computers in our society. For instance, the current desktop interface composed of the Windows operating system, icons, mouse, and pointer (a.k.a. WIMP) made computing accessible to the masses. The experiential nature of virtual reality interfaces will revolutionize the way we absorb and acquire knowledge in the near future. One of the sources of confusion regarding the concept of VR is how different it is from 3D PC/console games, or from the yber world of Internet communities. Broadly speaking, 3D games are one type of VR system in the sense they provide a virtual experience of some sort. However, most 3D games, for commercial reasons, are still keyboard/mouse based or based on simple interfaces, and 3D game designers are interested in finding clever scenarios that are exciting and engaging so that they will attract and hook more players. VR scientists, on the other hand, are interested more in reproducing a given experience as faithfully as possible. For instance, a first-person shooting game should be exciting and engaging, while a virtual battleground (which might have almost the identical content) should be scary, and tense as in the real war. Another form of virtual reality is called ugmented Reality (AR). In AR, synthetic graphics/images/text are registered and overlaid onto the real scene (or on video imagery) using a special device known as a see-through head mounted display or a camera and image/graphics compositing system. In this sense, there is a continuum of R-ness, called Mixed Reality, in terms of how much of the displayed scene are real. In summary, virtual reality represents a new communication medium that is experiential and its technologies will allow users to interact with computers (or real, virtual or mixed reality worlds) naturally using many of our sensori-motor (or multi-modal) capabilities. While the general goals of virtual reality (to bring the human world into contact with the virtual world) and ubiquitous computing (to plant computing elements in our world) seem at odds with each other, our future living environment might actually look more like a mixed reality space with various displays, sensors and computing elements planted everywhere with people interacting with them effortlessly. In the next article, I will describe certain concrete applications of virtual and mixed reality. ABOUT THE AUTHOR Gerard Kim Joung-hyun is an associate professor in computer science and engineering at the Pohang University of Science and Technology (POSTECH), one of the top engineering schools in Korea. Prior to joining POSTECH, he worked as a computer scientist at the National Institute of Standards and Technology (NIST) where he was first introduced to the fields of virtual reality. He has since conducted research on virtual reality with particular focus on virtual presence, 3D multi-modal interaction and VR authoring tools. He has published over 70 articles on the subject in leading journals and international conferences such as he Presence, IEEE VR, and ACM VRST. Gerry Kim received his bachelor degree in electrical and computer engineering at Carnegie Mellon University, and his master and Ph.D. degrees in computer science at the University of Southern California. His personal and lab homepage can be found at www.postech.ac.kr/~gkim and vr.postech.ac.kr