Retro-commissioning (RCx) is a useful knowledge-based approach to restore a building to its optimal operations, resulting in high energy efficiency. In Hong Kong, the government has set high priority on retro-commissioning in the Climate Action Plan 2030+. The government and professional institutions, such as ASHRAE, BSOMES, EIHK, HKAEE, HKGBC, HKIE, HKPC, etc., have taken initiatives to promote RCx.