In the spirit of the first see-through head-mounted display developed by Ivan Sutherland, we and other researchers use the term "augmented reality" to refer to enrichment of the real world with a complementary virtual world. The augmented reality systems we are developing employ a see-through head-worn display that overlays graphics and sound on a person's naturally occurring sight and hearing. By tracking users and objects in space, these systems provide users with visual information that is tied to the physical environment. Unlike most virtual realities, whose virtual worlds replace the real world, augmented reality systems enhance the real world by superposing information onto it. The spatial tracking capabilities of our augmented reality systems distinguish them from the heads-up displays featured in some wearable computer systems.