We define occlusion-aware interfaces as interaction techniques which know what area of the display is currently occluded, and use this knowledge to counteract potential problems and/or utilize the hidden area. As a case study, we describe the Occlusion-Aware Viewer, which identifies important regions hidden beneath the hand and displays them in a non-occluded area using a bubble-like callout. To determine what is important, we use an application agnostic image processing layer. For the occluded area, we use a user configurable, real-time version of our previously published geometric model. In an evaluation with a simultaneous monitoring task, we find the technique can successfully mitigate the effects of occlusion, although issues with ambiguity and stability suggest further refinements. Finally, we present designs for three other occlusion-aware techniques for pop-ups, dragging, and a hidden widget.