This publication guides professionals confronting criminal or unauthorized acts involving nuclear or radioactive material. This publication is intended for individuals and organizations that may be called upon to deal with the detection of and response to criminal or unauthorized acts involving nuclear or other radioactive material. It will also be useful for legislators, law enforcement agencies, government officials, technical experts, lawyers, diplomats and users of nuclear technology. In addition, the manual emphasizes the international initiatives for improving the security of nuclear and other radioactive material, and considers a variety of elements that are recognized as being essential for dealing with incidents of criminal or unauthorized acts involving such material.