The European Union (EU) has set the objective to achieve a secure, sustainable and competitive energy. The development of a European energy policy is constantly emphasised in the declarations of EU political leaders. This thesis provides an assessment of the legal feasibility of an EU energy policy in the areas of industrial restructuring, institutional reform and security of supply. The first chapter looks into the Endesa saga, which offers a paradigmatic case concerning the tensions between energy champions and energy markets. Successive national and ‘foreign’ takeover bids for Endesa are examined at national and EU level by different authorities according to different legal regimes, which show the ambivalent contribution of the merger control to the development of an energy policy. The persistence of monopolistic structures despite energy liberalisation requires the reinforcement of the role of regulatory authorities, as analysed in chapter two. However, one cannot expect that national regulatory authorities and the newly created European Agency for the Cooperation of Energy Regulators enjoy the same powers and level of independence as their integration within Member States and the EU operates on the basis of different legal and institutional principles. Chapter three addresses security of energy supply, which is in principle a responsibility of the Member States (which often used it as a pretext to promote national champions), but it has also a European dimension in terms of external dependence and solidarity. The absence of a specific legal basis on energy in the treaties has not prevented the EU from dealing with security of supply by having recourse to legal bases in the fields of environmental policy, crisis management and trans-European networks. A more coherent approach to energy policy is expected with the new legal basis on energy in the Lisbon Treaty. Beyond future developments, this thesis measures the integrity of the commitment repeatedly expressed by European Heads of Governments and States to build up a European energy policy.