Book excerpt: This book was originally published by Claeys and Casteels, now formally part of Edward Elgar Publishing. Since the publication of the Fourth Edition in 2016 the EU's internal gas and electricity legislative framework has continued to develop quickly: A whole series of new Grid Codes have been adopted, including those on Capacity Allocation and, Congestion Management, on forward capacity allocation, on electricity balancing (EB), emergency and restoration, and on electricity transmission system operation. The Gas Directive has been amended, to bring pipelines connecting into the European system under the Internal Market rules on unbundling, regulated tariffs and third party access. The 'Electricity Market Design' package has been adopted, implementing new rules on balancing, capacity mechanisms, demand response, storage, the rights of consumers to participate in the electricity market and the powers and responsibilities of ACER. New exemption decisions for new infrastructure These changes mark a major evolution in the EU's Internal Market, as it pioneers the way towards a zero-carbon electricity system. The new volume continues to provide the standard industry reference work in this area, written by some of the key Commission Officials responsible for these developments, together with leading industry practitioners and academics.