Introduction : necessity and treaty obligations -- The doctrine of necessity in municipal and international legal orders -- The historical genesis of necessity doctrine : a conceptual descriptive -- Substantive and methodological issues in interpreting necessity clauses in treaties : a proposal -- Economic and national security emergencies : necessity clauses in international investment law and international trade law -- States of emergency in international human rights treaties -- Misapplying necessity : recent proposals in jus ad bellum and jus in bello -- Conclusion : necessity, sovereignty, and treaty interpretation.