This book provides a comprehensive analysis of national security exceptions in international trade and investment agreements. The subject has gained particular relevance in the past few years, as both the United States and the Russian Federation have invoked national security as justification for trade-restrictive measures in the context of WTO dispute settlement proceedings. The book describes the evolution of security exceptions in international economic law, from the GATT 1947 to the most recent economic treaties, such as the 2017 Buenos Aires Prool for Intra-Mercosur Investment and the 2018 USMCA. Further, it presents an overview of the rich array of adjudicatory practices addressing national security clauses, covering the decisions of WTO dispute settlement bodies, the ICJ, and numerous investment arbitral tribunals. To this end, the book addresses the debates surrounding the alleged self-judging character of security exceptions and the standards of review applicable where the exception is considered to be justiciable.