Radioactive substances comprise an area of research and method development in which FOI works to establish a scientific basis for assessments as to whether, in a given situation, radioactive substances can constitute a danger to people and, if so, what measures should be taken. Also covered is the development of radiological and nuclear (RN) forensic methods of working and analysis. The aim is to contribute to society’s ability to prepare itself for, and to manage, radiological incidents. The major customers in this field are the Swedish Armed Forces and other Swedish authorities but FOI also works with small and medium-sized businesses as well as with sister organisations and authorities in other countries. We also play an active part in Sweden’s national radiation protection emergency preparedness.