Terrorism is a serious issue that affects lives around the world. Is there a way to deter terrorists from engaging in terrorist attacks? According to the Federal Bureau Investigation (FBI), there are two types of terrorism to consider: domestic and international. For the purpose of this paper, international terrorism is defined as terrorism that takes place outside of the jurisdiction of the United States and domestic terrorism occurs in the United States (FBI, 2011). Terrorism has varying definitions depending on the country and agency enforcing terrorism laws. The United Nations does not have an agreed upon definition and Bruce (2013) argued that without an agreed upon definition, counterterrorism measures will not be effective. This paper will focus deterrence of terrorist acts by Islamic State of Iraq and Syria (ISIS) and Khorasan from a forensic psychological perspective.