Extending the tabletop to the third dimension has the potential to improve the quality of applications involving 3D data and tasks. Recognizing this, a number of researchers have proposed a myriad of display and input metaphors. However a standardized and cohesive approach has yet to evolve. Furthermore, the majority of these applications and the related research results are scattered across various research areas and communities, and lack a common framework. In this paper, we survey previous 3D tabletops systems, and classify this work within a newly defined taxonomy. We then discuss the design guidelines which should be applied to the various areas of the taxonomy. Our contribution is the synthesis of numerous research results into a cohesive framework, and the discussion of interaction issues and design guidelines which apply. Furthermore, our work provides a clear understanding of what approaches have been taken, and exposes new routes for potential research, within the realm of i...