For the purpose of this analysis, "mass casualty" bombings are defined as killing a minimum of 25 people, and bombings are considered "terrorist" if they are perpetrated outside of a state of war or if the targets are nonmilitary, regardless of the nature or motivations of the attackers. The time period addressed by this review extends from the end of World War II (August 14, 1945) to the end of the 20th century (December 31, 2000). This period was selected because it contained all of the known modern terrorist motivations, from anticolonialism to religious fundamentalism. Mass casualty bombings were found to have occurred on 76 separate occasions in the second half of the 20th century. In those attacks, 5,690 persons were killed, with an average of nearly 75 people killed per attack. At least 19 different terrorist groups have been identified as having perpetrated these bombings. The Tamil Tigers of Tamil Eelam (LTTE) have been the most prolific users of the mass casualty bombing attack. Hezbollah, a Shi'ite Muslim terrorist organization, has perpetrated fewer attacks, but with a higher total killed and a higher average killed per attack. When compared to other "new" terrorists, mass casualty bombers are more prolific than state-sponsored terrorists, more deadly than suicide terrorists, more identifiable than religious terrorists, and more plausible than CBRN (chemical, biological, radiological, and nuclear weapons) terrorists. Mass casualty bombers have long presented the greatest terrorist threat and will likely continue to do so in the future. 56 notes