The aviation sector represents an important transport industry and provides essential links between countries and regions. At the same time aviation is one of the contributors to the global greenhouse gas (GHG) emission.Given the trans-boundary nature of climate change, a global solution would be the most efficient and effective option for addressing the related GHG-emission. However, global negotiations so far have not been successful. Against this background, the EU has decided to include aviation in its Emission Trading System (ETS) from 2012. with this background, this book brings into focus the legality of EU aviation directive 2008/101 under GATT rules and the doctrine of sovereignty. Through analysis, the book addresses questions on whether EU aviation directive violates the doctrine of sovereignty reflected under Chicago Convention on International Civil Aviation Organization and the UN Charter, whether the unilateral and extraterritorial measure of EU can be justified under GATT rules and whether the GATT exceptions will be applicable to EU ETS scheme.