In its simplest form, reality is merely information that is presented or acquired. Mixed Reality (MR) is built around the integration of real world physical and computer generated virtual information. We do not use the term augmented reality (AR) because we view the merging of both worlds as a symbiosis, with desirable properties from each accentuated and complementing each other, rather than the enhancement of one with the other. Collaborative MR allows multiple participants to simultaneously share a physical space while being surrounded by a virtual space that is registered with the physical. Because the MR world inherits the properties of real and virtual worlds, it is rich with social context, spatial cues, and tangible objects from the real world as well as flexible digital information from virtual. We believe that Mixed Reality is a medium, largely unexplored, but very well suited for face-to-face collaboration.