Recent sweeping changes in European law in the energy sector have made issues of regulation of much greater importance than ever before. This book examines the legal and regulatory impacts of the very latest measures (2004) to open up EU energy markets to competition. It provides a comprehensive overview of the new rules--in theory and practice--and charts their consequences for the regulation of electricity and gas across the EU. It does so in two parts: first, at the European level, describing and analysing the rules and their impact on competition law; secondly, through a collection of detailed analyses of Member State legal regimes, written by recognized authorities from each country.