It is important to understand radon migration through and between the Earth’s “spheres”, e.g. atmosphere, hydrosphere, lithosphere and biosphere – for two main reasons. Firstly, this knowledge enables effective protection of people from the direct health hazard arising from the decay of radon and its daughter products. Secondly, as well as this direct hazard, this knowledge adds to our understanding of the mechanisms involved with other natural hazards such as earthquakes and volcanic eruptions. The papers in this special issue of Natural Hazards and Earth Systems Sciences represent a cross-section of the presentations made in the NH9.5 session Radon, Health and Natural Hazards at the 2009 European Geosciences Union (EGU) General Assembly, at which the International Geoscience Programme (IGCP) Project 571, Radon, Health and Natural Hazards was launched. This project has enjoyed a successful first year, culminating in a second session (NH8.3) at the 2010 EGU General Assembly, which drew a significantly higher number of presentations. We are grateful to everyone who has contributed, whatever the manner, to that success and look forward to the future.