The necessity to limit CO 2 emissions as well as the renunciation of nuclear power in many countries are the chief factors that determine the future development of electric power generation. These requirements can be met by integrating renewable energy sources, such as offshore wind farms and solar power from North Africa. However, in most cases, these renewable energy sources are far away from the load centers. This requires reliable long-distance power transmission systems. The HVDC transmission is the key technology to cope with this challenge in the future and therefore it is gradually gaining in importance. This paper gives an overview of the different state-of-the-art technologies in the field of HVDC transmission systems based on the HVDC schemes put into operation.