Two types of power electronic converter are used in HVDC: Line Commutated Converters (LCC) and Voltage Sourced Converters (VSC). LCCs are well-established and capable of handling very large powers at high efficiency. They also are able to electronically suppress and recover from DC line faults with no requirement to open mechanical switchgear, which gives them a considerable advantage in comparison with AC transmission. However, they require shunt reactive power compensation and harmonic filtering on both the AC and DC sides of the converter, leading to a very large site area, and in inverter mode they are susceptible to commutation failures when disturbances occur on the receiving-end AC system. They are also unable to feed power to a passive load without the aid of rotating machines to provide the commutating emf. VSCs are, at the time of writing, still not able to handle such high powers or achieve the same efficiency as LCCs, although the gap is closing rapidly. Several types of VSC exist but all are capable of feeding power to a passive load, do not suffer from commutation failures and are better able to operate on weak AC systems than LCCs. Their harmonic performance differs between types of converter but all are much better than LCCs, requiring only small harmonic filters (if at all). Most types, however, require switchgear (either on the AC or DC side) to open to clear DC line faults. This chapter presents a summary of the advantages and disadvantages of LCCs in comparison with several well-known types of VSCs.