It has long been suggested that any attempts to comprehensively define ‘terrorism’ will be unsuccessful and will not, in any event, add to our understanding of the term. This article refutes that position. It focuses firstly on the reasons why an internationally agreed definition is necessary, including the increased legal significance of the term as well as its continued abuse by states. The article then examines some of the main problems inherent in defining what many consider to be a subjective term. It concludes with an analysis of how these issues are reflected in the international debates of the United Nations.