There are certain challenges associated with a new HVDC facility when preparing the facility for commercial operation that are typically not present when doing the same for normal AC transmission facilities. HVDC facilities have more complex control and protection systems, unique primary plant such as DC measurement devices and high-speed switches, and more auxiliary systems that are critical to the facility’s operation than an AC transmission substation (such as air conditioning, air handling and water-cooling systems). They also have solid state power electronic equipment such as thyristors and IGBTs and may have long distance land and/or submarine cable systems. It is noted that increasingly, HVDC systems are being developed, installed, operated and maintained by smaller companies, private developers and sometimes single entities that do not already have established operation and maintenance (O&M) processes, staff and facilities. This is very different to the early days of HVDC development where the HVDC projects were largely built, owned and operated by established transmission utilities. For these smaller, non-utility or unestablished companies, the process of establishing the O&M philosophy, what skills are required, what activities would be beneficial to be insourced or outsourced and the timing of how these are developed and established (i.e. a roadmap) can be unknown. To be prepared to operate and maintain the new HVDC asset upon completion of its construction, installation and commissioning, O&M issues need to be considered as early as possible in the development of a new project to avoid potentially costly issues arising after commissioning of the systems. Late consideration can often lead to critical and costly issues, including being unprepared for various compliance issues and missing the unique training opportunities available during manufacture and construction for the staff expected to operate and maintain the asset going forward. This chapter provides general information about O&M practices followed by owners of HVDC converter stations. However, it is not a substitute for the development of detailed, comprehensive O&M instructions.