This book offers the first comprehensive assessment of the various internal and external measures undertaken by the European Union to guarantee security of oil and gas supply. It sets out and analyses in a coherent and thorough manner those aspects of EU external policy that are relevant in establishing a framework for guaranteeing energy security for the Union. What makes the book unique is that it is the first of its kind to bridge the gap between EU energy and EU external policy. The book discusses EU policy towards the major oil and gas producing countries of Russia, the Mediterranean and the Persian Gulf at the bilateral as well as regional and multilateral level. It brings together not only the dimensions of trade and investment but also other important aspects of external policy, namely development and foreign policy. The author argues that the EU's energy security cannot be achieved through adopting a purely internal approach to energy issues, but that it is necessary to adopt a holistic approach to external policy, covering efficient economic relations as well as development co-operation and foreign policies towards energy producing countries. The book will be a valuable resource for students of EU law, WTO law or international energy law, as well as scholars and practitioners dealing with energy issues.