Security has at least three facets. First, a security system must include physical security, which involves hardening the target against which an attack may be made. Second, a security system must have operational security, which aims to deny terrorists the opportunity to collect information on either the facility or its activities. Third, a security system must include personnel security, which focuses on the training of personnel to be responsible for security. In addition to the aforementioned security components, preventive security is also important. Such security is designed to make terrorist attacks less likely. One such security technique currently being used is the tagging and tracing of various weapon components. It is also possible, although not as easy, to use trace detectors for chemical agents, which would enable security agents to detect the presence of dangerous or hazardous chemicals in innocuous-looking containers. Given the costs, both monetarily and politically, of security measures, it is important to conduct a terrorist threat assessment to determine the extent to which a site is a likely terrorist target. There are three types of indicators that nations and individuals use to assess the threat of terrorism. These are general threat indicators, which are used to determine whether within the nation there are conditions that might stimulate or provoke terrorism; local threat indicators, which pertain to more specific and localized possibilities for terrorism; and specific threat indicators, which are used to assess the vulnerability of a particular target to terrorism. Until terrorism is believed to be enough of a threat to the economic well-being of both nations and industries to justify the expenditure of millions of dollars, security will remain a weak weapon in the arsenal against terrorism. Two case studies focus on airport security and the supplying of arms to Iran, a terrorist state. 5 suggested readings and 5 notes