Telepresence is a term used to describe an emerging medium that enables a person to feel as if he or she is physically present in a different place or time. 'Virtual reality' and 'artificial reality' are popular names for this field. Today, telepresence technology typically involves head-coupled stereoscopic displays, three-dimensional audio environments, and body- or hand-coupled input devices. Telepresence technology can provide the experience of being in two different kinds of spaces: computer-generated environments, and actual environments that are distant in space and/or time. The telepresence medium has inherited the rather contradictory traits of an obsession with photorealism from computer graphics and a penchant for metaphor from the realm of human-computer interface design. Its unique characteristics have also made telepresence and "virtual reality" the target of both fanciful and profound commentary from philosophers, feminists, ethnographers, and artists. Telepresence is thus an excellent context for discussing the evolving relationship between people and computer technology. This talk will begin with a definition of the idea of presence, a primer on enabling technologies and applications, and then will focus on critical research and design issues in telepresence.