Traditionally, HVDC links (or systems) were designed for very long-distance power transmission applications using overhead transmission lines, (several hundreds to a few thousand kilometers), long submarine cable links and interconnection between asynchronous systems. HVDC enables transfer of power for much longer distances than what is feasible using AC technologies because the transmission lines and cables do not by themselves generate or absorb reactive power. Advances in power electronics semiconductor devices, coupled with traditional HVDC features, may lead to a further deployment of this technology to improve system operation and support the development of onshore and, possibly, offshore transmission grids. Thanks to its speed and flexibility, the HVDC technology is able to benefit the existing AC transmission systems by improving the power transfer capacity, power flow control, transient stability, power oscillation damping, and voltage stability. HVDC links inserted into the AC systems could prevent cascading disturbances. Many HVDC application are not designed just to transfer power between two asynchronous AC systems, but instead, they are part of the AC Grids. These HVDC links are now referred to as “Embedded HVDC Systems”, which definition can be found in a CIGRE Technical Brochure, as: “An embedded HVDC system is a DC link with at least two ends being physically connected within a single synchronous AC network. With such a connection, it can perform not only the basic function of bulk power transmission, but also, importantly, some additional control functions within the AC network such as power flow control, voltage control, system stability improvement and the mitigation of system cascading failure.” Embedded configurations will be covered in this chapter as well as in Chaps. 30, “HVDC Scheme’s Dynamic/Transient Responses to AC and DC Faults,” and 31, “Dynamic/Transient Interactions with AC Network Components and Other Converters.” Also, relevant aspects to highlight the differences between the two existing HVDC technologies – the thyristor-based Line Commutated Converters (LCC) and the IGBT based Voltage Sourced Converters (VSC) are contemplated here.