This Practice provides an introduction to the electricity market in Great Britain (GB). It covers the principal organisations/types of organisation involved in the generation, transmission, international interconnection, distribution, and supply of electricity (electricity wholesale market, electricity retail market, and electricity networks market) in GB, as well as explaining the roles of key industry stakeholders. Given the complex structure of the GB electricity market, this Practice Note provides an overview of the key authorities and market participants in the GB electricity wholesale and retail markets. As the ownership structures of many market participants are often complex, where necessary this Practice Note simply refers to the parent company. Links to key sources/statistics are included, where relevant, as references in this Practice Note. However, for a consolidated set of links to key statistics published by DESNZ about the GB energy market, see Statistics at DESNZ. Brexit impact As of 31 January 2020 (exit day), the UK ceased to be an EU Member State, and at 11 pm (GMT)