There have been numerous unsuccessful attempts to define terrorism generically in international treaty law since the 1920s, from early conferences on the unification of criminal law to efforts in the League of Nations, the International Law Commission, and the UN General Assembly. While these sources do not carry great weight as evidence of customary law, they illustrate the recurring normative and political disputes surrounding definition and elucidate the basic features of an international prohibition and/or crime of terrorism, as perceived by different international actors. The recurrent attempts at definition indicate that the international community attaches considerable normative importance to it. Drafting of a UN Comprehensive Terrorism Convention continues in the Sixth Committee, and the UN High-Level Panel on Threats, Challenges and Change advocated definition in treaty law in late 2004. Generic definition of terrorism can capture and stigmatize the political motives which distinguish terrorism from ordinary violent crime, or transnational organized crime for financial benefit. Following an historical pattern, agreement on the scope of any exceptions to a definition of terrorism remains the key obstacle, although much of the argument about exceptions is ideological, not substantive.