Although the terms guerrilla and terrorist have been used interchangeably by many authors, they have different meanings. Guerrilla warfare is violent action taken within the normally accepted rules and procedures of international diplomacy and laws of war. In contrast, the violence in terrorism is directed mainly against civilian targets, and the terrorist's goal is publicity. To determine whether a particular event constitutes guerrilla warfare or terrorism, the motives, targets, acts, and effects must be considered. Genuine guerrilla organizations often lapse into acts of terrorism. A terrorist organization becomes an international terrorist organization when its goal involves more than one nation or deals with persons living in more than one country. The countries of origin of the membership, structure, and officers of an organization and the sources of support for the organization may also serve to define it as international. In addition, acts which take place against foreign officials and diplomats or carriers engaged in international commerce are also a part of international terrorism. The sharp increase in political terrorism -- terrorism used as an instrument of political action -- is one of the most disruptive elements in the contemporary western world. Political terrorism includes indiscriminate terrorism, discriminate terrorism, mass terrorism, and transnational terrorism. The Palestine Liberation Organization (PLO) is the best example of a transnational terrorist organization. The PLO example shows that transnational terrorist methods can achieve some success. Although nations cannot eliminate terrorism, they can take such measures as making no deals and minimizing publicity about terrorism. Sixty-five footnotes are provided.