Terrorism is a permanent challenge for the Rule of law, which must fight it without questioning its base of liberal principles. After September 11th, Anglo-Saxon countries, whose legal systems rejected the notion of ‘exceptional circumstances’, have immediately passed security legislations, which were often quite detrimental to the very principles governing the « due process of law ». In written law countries, such as France, legal systems have often perceived terrorism as an exceptional phenomenon, fit to be faced with emergency provisions. Today, one can observe a leveling in approaches, as security legislations tend to become perennial and the fight against terrorism becomes a contextual element in all legal systems. Beyond this, a true ‘opportunity effect’ of the terrorist threat is developing, allowing to justify security provisions that are often far removed from the necessities of the fight against terrorism, but that can be justified by the latter. One can then wonder whether the Rule of law would not be threatened more by the restrictions it brings on the liberal principles that form its foundation rather than terrorist movements’ blind violence.