Many harms flow across the ever-more porous sovereign borders of a globalizing world. These harms expose weaknesses in the international legal regime built on sovereignty of nation states. Using the Trail Smelter arbitration, one of the most cited cases in international environmental law, this book explores the changing nature of state responses to transboundary harm. Taking a critical approach, the book examines the arbitration’s influence on international law generally and international environ- mental law specifically. In particular, the book explores whether there are lessons from Trail Smelter that are useful for resolving transboundary challenges currently confronting the international community. The book collects the commentary of a distinguished set of.