We introduce a shadow-based interface for interactive tabletops. The proposed interface allows a user to browse graphical information by casting the shadow of his/her body, such as a hand, on a tabletop surface. Central to our technique is a new optical design that utilizes polarization in addition to the additive nature of light so that the desired graphical information is displayed only in a shadow area on a tabletop surface. In other words, our technique conceals the graphical information on surfaces other than the shadow area, such as the surface of the occluder and non-shadow areas on the tabletop surface. We combine the proposed shadow-based interface with a multi-touch detection technique to realize a novel interaction technique for interactive tabletops. We implemented a prototype system and conducted proof-of-concept experiments along with a quantitative evaluation to assess the feasibility of the proposed optical design. Finally, we showed implemented application systems of the proposed shadow-based interface.