This session will focus on a variety of impacts and hazard-associated manifestations of radon gas and is a development of the EGU 2009 meeting, with focus specifically on a recently established IGCP Project 571. Radon has a major significance for human health as the second leading cause of lung cancer. As well as being a hazard in its own right, there is evidence that radon concentrations (e.g. atmospheric, soil-gas and groundwater) can be used as a diagnostic of crustal geophysical processes and, hence, associated geohazards. For example, recent researches have revealed radon anomalies observed as possible earthquake precursors. A link has also been demonstrated between ocean and earth tides and built-environment radon levels in some locations. Due to radon emanating from rocks and soils, there are also archaeological aspects which include links between (ancient) mines and the health of miners, cave dwellers (historical and modern), cave visitors / guides and archaeological excavations / excavators. This session will present a broad range of papers including methodological, technlogical and interpretative aspects, as well as case study material.