This book offers an in-depth analysis of the WTO security exceptions and relevant rulings by WTO dispute settlement panels. The WTO security exceptions are commonly regarded as the "box of Pandora" of the WTO system, since WTO Member States can invoke them in order to justify trade restrictions violating WTO law which they consider necessary for their essential security interests. The Members of the WTO and the GATT 1947 have hesitated for decades to rely on these security exceptions. In recent years, however, these clauses have been invoked for the first time in high-profile disputes involving Russia and Ukraine, Saudi Arabia and Qatar, as well as the US, China, the EU and other nations. This has been regarded as the turn of an era in view of the risk that the security exceptions could be instrumentalized to undermine the WTO and the international economic governance system more generally. This study therefore thoroughly analyses the WTO panel reports issued in these landmark cases. It also explains the geopolitical relevance of the increasing invocation of security clauses and argues that the legally and methodologically sound application of the WTO security exceptions, which have often been regarded as "self-judging" provisions, requires a proportionality analysis encompassing tests of the suitability and necessity of the trade measures to be justified under these truly exceptional clauses.