OmniTouch is a body-worn projection/sensing system that enables graphical, interactive, multitouch input on everyday surfaces. Our shoulder-worn implementation allows users to manipulate interfaces projected onto the environment (e.g., walls, tables), held objects (e.g., notepads, books), and even their own bodies (e.g., hands, lap). This approach allows users to capitalize on the tremendous surface area the real world provides. For example, the surface area of one hand alone exceeds that of typical smartphone; tables are often an order of magnitude larger than a tablet computer. If these ad hoc surfaces can be appropriated in an on-demand way, users could retain all of the benefits of mobility while simultaneously expanding the interactive capability.