Since its invention millenia ago, paper has served as one of our primary communications media. Its inherent physical properties make it easy to use, transport, and store, and cheap to manufacture. Despite these advantages, paper remains a second class citizen in the electronic world. In this paper, we present a new technology for bridging the paper and the electronic worlds. In this new technology, the user interface moves beyond the workstation and onto paper itself. We describe paper user interface technology and its implementation in a particular system called XAX.