Electric power is generated and transported globally by the means of an “Alternating Current” (AC) process. However, there are some applications in which “Direct Current” (DC) power transmission is superior to AC. Problems due to the lack of technology that provides good control and regulation for conversions of DC-to-AC and AC-to-DC hampered deployment of DC power transmission technology. The development of power electronic devices has removed a large portion of restrictions on “High Voltage Direct Current” (HVDC) power transportation. HVDC use has become part of daily use for a long time due to its economic benefits and technical advantages over the “High Voltage Alternating Current” (HVAC) power transmission. The advantages of HVDC make it suitable for power transmission over long distances and for connecting power systems of countries operating at different frequencies. This paper introduces the principles of HVDC, compares the applications of HVDC in the world, and discusses the future improvements needed within this technology.