The purpose of the nuclear security regime is to prevent, detect and respond to nuclear security events (e.g. illicit trafficking of nuclear material or a nuclear terrorism attack). Nuclear forensic analysis is a key technical capability that utilises signatures inherent to nuclear or other radioactive material to provide information on its source, production and history. It can be used as part of the response to the nuclear security event, as well as to help prevent it. Section I of this article will introduce the basic information about nuclear forensic analysis.