In recent years, counter-terrorism measures have notably reshaped the relationship between terrorist suspects and the state. In this context, the discourse surrounding the lack of a uniform and comprehensive definition of terrorism at the international level has reoccurred. In the course of this contribution, clear lines will be drawn between the lack of an international definition of terrorism and certain transnationally important domestic trends relevant to the definition and countering of terrorism. Each section will focus on a particular aspect of the debate surrounding the term ‘terrorism’ with the aim of contextualising the development of the definitional vacuum and its impact on state counter-terrorism particularly after 9/11. It will be argued that an internationally binding definition of terrorism might not in fact have an impact on state counter-terrorism measures and domestic definitions of terrorism. This contribution will conclude that in the context of domestic and transnational legislative developments following 9/11, even if a definition of terrorism existed in international law, in practice there is no certainty that states will comply with it both in times of normalcy and emergency.