This Guide offers guidance on practical measures for reducing radon levels in workplaces. It is aimed principally at employers and those who control buildings used for work purposes. The guidance should also be of interest and assistance to surveyors and builders concerned with specifying and carrying out the necessary remedial measures, and environmental health officers and health and safety inspectors policing legislation. Guidance is provided to help non-professionals identify different types of building construction, how to test a building for radon and practical solutions to reduce radon levels if they exceed acceptable levels. It aims to provide practical cost effective solutions that will reduce indoor radon levels sufficiently to enable the employer to comply with the requirements of the Health and Safety at Work act and Ionising Radiations Regulations 1999.