Terrorism has become a grave phenomenon that threatens the daily lives of people anywhere in the world. Furthermore, the criminal phenomenon is no longer local or regional aspect associated to a state or culture, but the fact that confirmed by events at every moment that terrorism phenomenon has no country, religion or identity. As a result of the spread of terrorism acts, at the international level, the international community as a whole realized that terrorism has become a strategic threat to all states. So, concerted endeavors have been made to find ways and means capable of preventing and suppressing international terrorism Therefore, the objective of this study is to clarify the provisions and rules of Public International Law, by clarifying the legal concept of terrorism and mechanisms of combating it and all the consequences related to that. The study includes three chapters and a preamble - that examines the real aspect of terrorist activities and the international efforts to combat it. First chapter deals with what are terrorism, its definition in jurisprudence and convention, and its concepts in national legislation. However, the second chapter highlites the international mechanism to combat terrorism through the obligations were imposed on states under conventional international law, and the measures which adopted by the United Nations. While the third chapter discusses the international responsibility to fight, terrorism by showing the violation, the attribution of violation for the state and the legal consequences of the state responsibilities. The most important findings and recommendations will be reviewed in the conclusion.