Although natural sources of radiation are not usually of regulatory concern, some exposures to radon and naturally occurring radioactive materials (NORM) may warrant consideration as to whether controls should be applied. More and more countries are regulating exposures to natural sources, and the body of radiological data on such exposures is growing rapidly. This international conference, NORM IV, is the fourth in a series dating back to 1997, and also follows on from an international symposium held in Rio de Janeiro in 1999 (the proceedings of which were published as IAEA-TECDOC-1271). Among the topics addressed at NORM IV were exposure to radionuclides of natural origin in mining and other industrial operations involving NORM (including environmental impacts), standards and regulation, and measurement techniques including measurement of radon. In line with the IAEA’s safety related programme objective to foster information exchange, this publication is aimed at disseminating important new information on exposure to natural sources to a wide spectrum of technical and regulatory personnel working in this area.