Terrorism did not begin in the twenty-first century; terrorism has been around since the beginning of civilization. Nor is terrorism particular to a single political, economic, or religious identity. This chapter will focus on twenty-first-century terrorism, which is predominantly, but not exclusively, attributed to Muslim extremism. Terrorism is a tactic, used by a group, to instill terror in an audience in order to attain political, economic, or identity goals. In this short volume, we have already seen terrorism as a tactic used by the National Liberation Front in Vietnam, the Irish versus the British Crown, Jewish insurgents during the British Mandate in Palestine, and in Central America, which was characterized by political insurgency. Most frequently terrorism is used by a weaker group to fight against a stronger group in order to overturn the existing political or economic order. The terrorist group gains an identity by terrorizing the established government. In the twenty-first century, according to such theorists as Mary Kaldor, terrorism is used at its most basic level to upset the existing order by introducing chaos into a stable system. 1