Security exceptions are aimed at ensuring a margin of discretion for the adoption of sovereign decisions in questions of national security. To-date, most States consistently incorporate such exceptions into their economic treaties. Yet, treaty language has changed over time. At least three generations of security exceptions can be identified in post-SecondWorldWar trade and investment agreements. These generations broadly reflect attitudes towards trade liberalization and international decision-making, which prevailed in different historic settings. Few words are as powerful as security. Any room for discussion ends where ‘security reasons’ are invoked. The call of ‘security’ entails a warning not to ask, not to inquire, and not to doubt. This holds true not only for police measures in airports and train stations. Security often takes on a similar role in international affairs and, more particularly, in the arena of international trade. Policy-makers too often rely on national security to justify restrictive policy choices. The past few years bear witness to the growing use of security as an ultimate means of justification. Examples appear all over the field of international economic law, from WTO disputes on the United States’ imposition of tariffs on aluminum and steel1 to investment claims on the use of India’s electromagnetic spectrum