The purpose of the commissioning process for HVDC systems is to confirm that all systems and components in the HVDC system are designed, installed, tested and can be operated in accordance with their functional and operational requirements, to confirm that the behavior of the HVDC system and its various components are as expected, and to prepare the HVDC system for handover for operational service. The commissioning of an HVDC system commences after the design, factory testing, installation and site equipment tests for all converter station equipment and various subsystems have been completed. These activities are performed on-site, at all converter stations associated with the HVDC system. This chapter describes the testing and commissioning process typically undertaken for HVDC systems, and presents the typical tests performed during commissioning. It also discusses some of the challenges that could be expected during commissioning, key aspects of the planning, performance and finalization of commissioning activities and the transition from commissioning to operation. This chapter does not cover the testing and commissioning of the DC transmission line or underground/subsea cables.