How should a WTO panel react when faced with the argument that an allegedly WTO inconsistent trade restriction is justified under an environmental treaty, IMF rules or customary international law? How should they react when parties make objections, claims or defences based on rules of general international law, not explicitly covered in the WTO treaty itself, such as rules on burden of proof, standing, good faith, due process, error in treaty formation or the binding nature of unilateral declarations? Those are the type of questions that gave rise to this book. They are very real and practical questions and as a legal adviser to WTO panels, I was often asked to answer them. In the US – Shrimp dispute, for example, the United States invoked a number of multilateral environmental treaties in defence of its import ban on shrimp coming from countries which, in the US view, did not sufficiently protect endangered turtles.