The radioactive noble gas radon-222, characterised by a halflife of approximately 3.8 days, is produced by the alpha disintegration of radium-226 in the uranium-238 decay chain. Radon, released from rocks and soils to the atmosphere, is an important health hazard (Darby et al., 2004), and an important tracer of geophysical processes (Tanner, 1964), able to reveal meaningful information to reduce natural hazards, including volcanic eruptions and earthquakes (Laiolo et al., 2012; Neri et al., 2011; Plastino et al., 2011; Gillmore et al., 2010). The session NH8.3 Radon, Health and Natural Hazards at the 2010 European Geosciences Union (EGU) General Assembly provided a vivid illustration that understanding radon in natural and man-made environments remains the subject of applied and fundamental research. This special issue is dedicated to results presented at this EGU session and marks the second year of the UNESCO IGCP Project 571 “Radon, Health and Natural Hazards”.