The September 11, 2001 attacks and the "war on terror" declared by the United States in response to those attacks have ignited interest in "transnational armed groups". One of these groups, Al Qaeda, was responsible for the attacks and is the main, declared enemy in the "war on terror". It is uncontroversial to state that international terrorism represents a considerable challenge to the international community and that international law must meet this challenge. What is controversial is whether this challenge must, or at least may, be met by classifying terrorism as "war" or, in the terminology of contemporary international law, as "armed conflict". Similarly, can the enemy engaged in such a war be duly regarded as an "armed group"? The two questions are interrelated, as an armed conflict cannot exist without two or more parties which must be either states or armed groups. The result or, for some, the aim of such a classification as an armed conflict would be the application of the law of armed conflict, which, in conformity with contemporary practice, I prefer to call international humanitarian law (IHL).