This book critically examines the extension of EU environmental legislation beyond EU borders through measures that determine access to the single market on the basis of processes that take place in third countries. It makes a timely contribution to political debates about the relations between EU and non-EU countries, and the Union's role in the global governance of environmental policy, where it has been considered a global leader. The book aims to identify and explain the emerging legal phenomenon of internal environmental measures with extraterritorial implications as an important manifestation of EU global regulatory power, and assesses the extraterritorial reach of EU environmental law from a legitimacy perspective. It examines mechanisms that can bolster its legitimacy, focusing on the legal orders of the EU and the World Trade Organization, which are key legal fora for controlling the EU's global regulatory power.