This Module introduces students to key concepts, principles, instruments and institutions underpinning criminal justice responses to terrorism, as envisaged in the United Nations CT Strategy. It also explores some of the underpinning reasons for, and implications associated with, there being no universal consensus regarding a definition of terrorism. Furthermore, it introduces students to the notion of international criminal law, in addition to different types of jurisdiction to prosecute serious international crimes, including those related to terrorism. Since issues relating to the fairness of trial proceedings are examined in Module 11, Module 4 focuses principally on substantive and some procedural elements of prosecuting individuals for terrorist acts, whether as treaty-based crimes of terrorism or as core international crimes. Although the presumption is that institutions generally operate within applicable legal frameworks, on occasion human rights violations can occur, some of which may involve the commission of crimes by State officials, themes which are explored in Module 14.