This CIGRE Green Book presents an overview of the operation of distributed energy resources (DER) and their role in enabling active distribution networks. The content draws on the expertise and work of CIGRE?s Study Committee C6 (Active Distribution Systems and Distributed Energy Resources) and is the result of five years of development by the committee?s working groups. The book includes descriptions of DER assets, network systems, planning and operation, rural and off?grid systems, and future prospects. By describing international developments and providing several examples of DER applications, it serves as a valuable guide for researchers and practitioners interested in the subject. Readers who would like to comment on any of the published books or identify errors to the editorial team please contact:[email protected].