Recent technical developments in the smartphone and tablet market show that the fusion of input and output within a single device leads to a more direct and natural interaction. While the majority of research focuses on techniques based on touch-sensitive 2D surfaces, we aim at extending the design space to the physical 3D volume above a tabletop. For this purpose, we present spatially aware handheld paper displays as a promising approach that utilizes this space. By using the physical position and orientation of such paper displays (tangible lenses), users can experience a very direct and tangible way of interacting with various types of complex virtual information spaces. The simultaneous use of multiple tangible lenses in different shapes and sizes explicitly supports collaborative work. In this work, we present basic concepts for interacting on and with tangible lenses, discuss concrete application scenarios, compare active and passive displays, and outline the principle setup of our technical system.