This book is an attempt to approach the issue of defining international terrorism, proposing that the most workable way to do so is to achieve due balance between the two principal driving forces of international law developments: State sovereignty interests and cosmopolitan ideals. All those who aspire to the promotion of international criminal justice and the fight against impunity agree that the formulation of a universal definition of international terrorism will further enhance the fight against terrorism and offer a universally acceptable legal framework within which this fight can be conducted. Discussed in an in-depth manner are, for instance, the UN Charter Provisions, the Rome Statute and the principle of complementarity, the Kampala amendments on the crime of aggression, the paradigms of aggression and terrorism, and prominent anti-terrorist Security Council Resolutions such as Resolution 1368 and Resolution 1373. The volume broadens the reader’s understanding on how State sovereignty interests and priorities as well as ideals of cosmopolitanism have influenced the development of international law in general and international criminal law in particular. Furthermore, it simplifies the complicated picture of defining international crimes by expla ining how the ‘State sovereignty’ and ‘Cosmopolitanism’ dynamics have also been of relevance throughout the drafting process of the definition of the crime of aggression for the purposes of the Rome Statute for the International Criminal Court. In addition, it equips the reader with an understanding of the reasons behind the lack of an international definition for terrorism and suggests an appropriate context within which such a definition can take shape.