Terrorism is not a new subject by any stretch of the imagination. “Each year, terrorist groups commit hundreds of acts of violence.” This is the sentence with which the authors started the section in terrorism in the ﬁrst edition of this book 6 months before the attack on the World Trade Center in New York City and Washington DC on September 11, 2001. That day was the single most brutal and coordinated attack by a foreign terrorist group on U.S. soil, far worse than the ﬁrst strike on the World Trade Center in 1993 led by Ramzi Yousef. The 9/11 attack was, for many, unimaginable. After this date, Americans were bombarded with information and images of al-Qaida, the group that perpetrated the attack. September 11, 2001 changed the way Americans dealt with terrorism psychologically. Americans had a steep learning curve and a higher threat perception of al-Qaida, and in turn the U.S. government stepped up its counterterrorism initiatives and policies. Terrorism, no matter where it is perpetrated, can have a profound eﬀect on the mind set of a targeted population.