This paper presents a comprehensive review of existing research and development work on Voltage Sourced Converter (VSC) based HVDC systems. In addition to providing an overview of the state of the art, an extensive bibliography of the existing literature is provided. Throughout the paper numerous areas of open research are also identified to promote future development of this promising technology. Index Terms--VSC, HVDC, Multilevel converters 978-1-4244-4241-6/09/$25.00 ©2009 IEEE