The control and operational principles of HVDC transmission are briefly reviewed. Basically no telecommunication is necessary for operation, with the exception of telephone connections. As the demand for service and system control increases, telecommunication requirements will grow. General requirements of telecommunications are summarized and specific requirements regarding signal speed and volume and channel bandwidth are listed for different purposes, for instance, link operation, protection, and frequency control. Multiterminal arrangements are considered from a telecommunications viewpoint. Different transmitting media, e.g., line carrier and microwave, are discussed. It is shown that the capacity of line carriers transmitted on overhead dc lines will normally be sufficient whereas long cables may demand further measures.