The illegal transport of conventional explosives and biological material has been observed in public mail and could lead to serious health hazards. In response to Member State requests to establish guidance on detecting the movement of radioactive material in international mail, the IAEA and the Universal Postal Union (UPU) undertook a joint effort to prepare this publication. It considers how radioactive materials in international mail might be detected, how best to monitor for these materials in mail facilities and how to respond appropriately. This publication provides a concise but comprehensive description of the various techniques and equipment used to detect and control radioactive material during mail processing.