Illicit trafficking of nuclear and other radioactive material poses a serious threat to the global safety and security. The European Commission’s Joint Research Centre (JRC) provides analytical support and develops improved methods to strengthen nuclear security at the level of competent national authorities and international organizations. With its expertise in nuclear forensics, the JRC enables EU Member States and other interested parties to adequately respond to nuclear security events and make informed decisions on the threats associated with nuclear and other radioactive materials out of regulatory control. This report aims at familiarizing decision makers and the general public with the nuclear forensics casework performed at the JRC in support to EU Member States and other partner countries. Using non-scientific language, the report presents a comprehensive overview of the scientific field of nuclear forensics, explaining its basic principles and its relevance. Next, it takes a closer look into five selected cases that the JRC investigated during the 30 years of its involvement. The report’s purpose is to highlight the importance of having this capacity within the European Union, which enhances consequently the security of the European citizens.