There is a common ideology that links all terrorists, regardless of their desired goals: the understanding of the utility of terror as a tool for change. The author uses terrorist writings from the 18th, 19th, and 20th centuries to show the uniformity of thought in the writings regarding the use of terror as a tool to achieve desired social change. The historical and contemporary writings by Maximilien Robespierre, Johann Most, Osama bin Laden, the Army of God, the Animal Liberation Front, and the Earth Liberation Front show that while there are differences between terrorists, the utility of terror as a means to cause social change is common to all terrorists. It is contended that the terrorism of the 18th and 19th centuries involved selectivity in its targeting, but that modern day terrorism has eschewed selectivity and instead uses terror to achieve high victim mortality rates. The use of explosives by terrorists is examined and has been philosophized to cause a positive psychological reaction on terrorists, regardless of the outcome to the target of terror. Next, the author looks specifically at the task of defining terrorism and argues that the central aspect of terrorism is the intention and circumstances of the act of terror, not the outcome of terror. Thus, while the causes of terrorism change, the utility of terror as a means to achieve a desired goal never changes. Notes, references