This article addresses the definition of terrorism. It is intended to provide a foundation from which to understand the recent attacks on the World Trade Center and the Pentagon. Although terrorism appears to be much less dangerous than other forms of violence, it seems to command more attention. In order to respond to terrorism, a clear definition is necessary. Terrorism is defined by Title 22 of the U.S. Code as politically motivated violence perpetrated in a clandestine manner against noncombatants. Experts on terrorism also include another aspect in the definition: the act is committed in order to create a fearful state of mind in an audience different from the victims. Whether or not an act is considered terrorism also depends on whether a legal, moral, or behavioral perspective is used to interpret the act. If a legal or moral perspective is used, the values of the interpreter are the focus rather than the act itself. A behavioral perspective appears to be best suited for interpreting and reacting to terrorism.