Gravity sensing, gravity-dependent signaling pathways and resulting graviresponses are found even in single cells as shown in studies on unicellular animal and plant model systems. Although the gravity-dependent responses of single-celled systems are obviously very different, the presented experimental data from experiments on ground and in space reveal that especially the early phases of gravity sensing share common features. The gravisensory processes can be reduced to two principles: perception via intracellular statoliths and via the whole protoplast. Gravisensory ion channels and cascades of ubiquitous second messengers are proposed in most gravity-dependent signaling pathways and have been identified in some cases. Cytoskeletal elements have been shown to play a master role in the complex processes of gravity sensing and graviorientation. Research on ground has been complemented with experiments in microgravity, which greatly contributed to our understanding of gravi-related signaling processes.