[Page 827]Some acts of violence are labeled terrorism. Yet, the victims as well as perpetrators will sometimes dispute this label. Not only are those directly involved often in disagreement, but even different countries will have different official definitions of terrorism, as do various security agencies within the same country. It should be no surprise, therefore, that academics have not reached a consensus on the definition of terrorism. These disparities also extend to the explanations provided by researchers as to how people become involved in terrorism. Indeed, many scholars have offered various theories and models to suggest which psychological factors influence a person to legitimize the use of terrorism. After addressing the question of how terrorism is to be defined, this entry reviews the most popular ...