The nuclear security summit of April 2010 aimed at enhancing international cooperation to prevent nuclear terrorism, an issue that has been identified as the most immediate and extreme threat to global security. International cooperation at the scientific, technical, and operational level is of key importance for sustainable success in combating illicit nuclear trafficking and nuclear terrorism. The three main steps related to combating illicit trafficking are prevention, detection, and response. If prevention fails and nuclear material is detected (through measurement systems or by intelligence), an appropriate response has to be initiated. An essential element of the response process is to provide clues on the origin and intended use of the material (that is, nuclear forensic investigations). The results serve for prosecution and for improving the control of nuclear material at the source (for example, physical protection and safeguards) to prevent future thefts or diversions. This timely session spotlights the forensic science, tools, and tactics operated by the European Union, the United States, and the International Atomic Energy Agency. Speakers will focus on concrete examples to demonstrate how seized nuclear material is analyzed and explain cross-border capacity-building measures. The session will equally underscore current scientific challenges and the extent of ongoing international cooperation.