HVDC converter stations, as is the case for all power plants and power transmission systems, must be controlled protected and monitored to provide the operators and maintenance crews with information to ensure that the converter stations are safely operated and properly maintained. The measured quantities of the input and output of HVDC converter stations however cannot be directly connected to the protection and control systems due to the nature of these signals. Many different types of measuring equipment or devices are therefore installed in the converter stations to support these functional requirements. Much of the measurement equipment entails measurements of voltages, currents, electric power etc. but status information is also needed to support operators and for automatic switching functions. Some of the measuring equipment is identical to what is used in conventional AC substations but measurement of DC quantities is uniquely associated with HVDC converter stations. The introduction of voltage source converter (VSC) systems has increased the use of HVDC technologies. The result is more research and development (R&D) of new technologies for measuring DC currents and voltages in HVDC systems. The chapter, therefore, is focused on measurement fundamentals and existing technologies to the degree that they are known and well documented. Furthermore, metering transducers in gas insulted switchgear (GIS) are not covered here.