Particularly after the Datagate revelations, the clash between privacy and security has become one of the most controversial topics of our time. This paper deals with this topic from a comparative perspective, looking at the balance between data protection and national security provide by EU and US constitutional systems. Following the adoption of the Charter of Fundamental Rights of the European Union, the EU would appear to guarantee a high degree of privacy protection. By contrast, in the United States privacy protection has weakened as the technology used in combating international terrorism has improved. The two systems clearly differ in approach but comparing them also brings to the surface various points that could be useful in defining a common, global approach to privacy.