The authors review the advantages of high-voltage DC transmission, and discuss the benefits that the use of voltage-sourced converters could bring. They start by giving a simple representation of an HVDC interconnection and then discuss the use and benefits of HVDC for bulk power transmission, power transmission via cables, termination between unsynchronised AC systems, parallel AC/DC transmission, and minimising short circuit capacity increases. New power semiconductor devices for HVDC are discussed, in particular, the voltage source converter and its applications in HVDC for rotating machines and reactive power control.