Statistics of people forced from their homes and their country provide a troubling measure of social malaise. Among its causes is terrorism. This week, from a figure of 20m just over a decade ago, the number of internal and external refugees reached 65.3m. In a recent Address Professor Keith Hayward stated: “Terrorism, civil unrest, seemingly unstoppable immigration, cyber-activism, a growing ‘precariat’ [people living a precarious existence, without security or predictability, especially job security], the rise of ‘theistic violence’: these, and other portents, suggest a gathering storm of global discontent and rancorousness”. In his report last year to the British Government its Independent Reviewer of Terrorism Legislation, David Anderson qc, advised: The highest priority risks are in summary: terrorism …” In its Government Report On Counter-terrorism Efforts the Danish Government stated: “The Government’s objective is to protect the population against terrorist acts in Denmark, to prevent terrorism by addressing its root causes, to ensure that the counterterrorism efforts are carried out in full in accordance with international law … This report mainly focuses on counterterrorism developments over the past year, both nationally and in international cooperation.” In Le Monde on 1 April 2016 « Le Caractère global du terrorisme appelle une justice globale » Mireille Delmas-Marty wrote: « Clearly a merely national response, however secure, cannot by itself deal with the entire threat.” Having left Nazi Austria in 1937, Karl Popper concluded in The Open Society and its Enemies “… progress rests with us, with our efforts, with the clarity of our conception of our ends, and with the realism of their choice”. In 2015 there were 11,774 terrorist attacks that killed 28,300 people. Yet the authoritative report by the International Bar Association’s Task Force Terrorism and International Law advises there is no internationally agreed definition of what legal elements a definition of terrorism should possess. The attempt at such definition by the 1937 International Convention for the Prevention and Punishment of Terrorism adopted under the auspices of the League of Nations was never implemented. Throughout the subsequent eight decades those responsible at international level for agreeing and enforcing such definition have failed to achieve agreement. They have now reached a point of inertia. This paper will address these issues.