This collection of essays examines and reassesses the basic principles of EU foreign relations law that have emerged over 50 years of incremental Treaty-based and judicial development. It also explores the particular character of the EU's 'external constitution.' The essays have been written against a background of change, and they debate: the deliberation over the character of the appropriate constitutional framework which has surrounded the drafting of the Constitutional and Reform Treaties, the increasingly cross-pillar nature of much EU external action, and renewed interest in the accountability of foreign relations policy and practice to democratic and judicial review within and without the EU. In exploring the legal context in which the EU seeks to develop an international identity, and to structure and execute policies at the international level, the collection will interest those working in international relations.