The United States Department of Defense defines terrorism as "the calculated use of unlawful violence or threat of unlawful violence to inculcate fear; intended to coerce or to intimidate governments or societies in the pursuit of goals that are generally political, religious, or ideological." While terrorism has been around for centuries, it was the al Qa'eda attacks of September 11, 2001, that brought home to the world, and most particularly the United States, just how dangerous terrorism can be. The third edition of the Historical Dictionary of Terrorism presents the full spectrum of forms of political violence through a chronology, an introductory essay, a bibliography, and hundreds of cross-referenced dictionary entries on major terrorist groups and their leaders, significant terrorist events, cyber-terrorism, counterterrorism, and social science concepts regarding the motivations and group dynamics of terrorist groups. Authors Sean K. Anderson and Stephen Sloan move beyond the gut reaction we have to this volatile and divisive topic by providing a reliable and objective reference on terrorism.