Tangible user interfaces (TUI’s) bridge the divide between the physical and digital worlds . They marry the interactivity of the digital world with our embodied cognition of the physical world and, in doing so, permit intuitive forms of human-computer interaction . As TUI’s research and development continues apace, the boundary between the physical and digital worlds is becoming increasingly blurred. Physical objects now replicate the functionality of GUI’s and add new modes of interaction to our physical environments. As Weiser predicted, computer technology is becoming increasingly embedded into the fabric of our physical space.