Terrorists' physical attacks on diplomats and their families have increased the difficulty of recruiting qualified persons to the diplomatic service and prompted the establishment of personal and facility security measures that have reduced the accessibility of diplomatic services. Terrorists' ignoring of the traditional immunity from attack granted the diplomatic corps of all nations threatens to undermine the diplomatic system by preventing diplomats from performing their intermediary functions. Terrorism against diplomats creates a number of problems in foreign policy. Where such terrorism is state-supported, it constitutes an indirect hostile and violent engagement that undermines peaceful relations between the involved countries. Terrorism against diplomats by nonstate-supported terrorists presents another foreign policy problem, that of the host country bearing responsibility for protecting foreign diplomats. Also, there is the problem posed by a terrorist situation that complicates bilateral or multilaterial relations among nations, such as the Basque terrorist problem which complicates relations between France and Spain because they share a common border used by the Basques for their own ends. In dealing with the problems posed by terrorist attacks on diplomats, each nation must decide how it will work with other governments. Cooperation can include the exchange of intelligence information, joint planning to address terrorist attacks, cooperation in specific incidents, and cooperation in the pursuit of terrorists. The establishment of international agreements which express a consensus about acts that are crimes under international law is an important tool for mobilizing international cooperation against terrorism. The enforcement of the agreements, however, is dependent on changing political realities. Seven footnotes are provided.