Building commissioning (Cx) is the process of verifying, in new construction, all (or some, depending on scope) of the subsystems for mechanical (HVAC), plumbing, electrical, fire/life safety, building envelopes, interior systems (example laboratory units), co-generation, utility plants, sustainable systems, lighting, wastewater, controls, and building security to achieve the owner's project requirements as intended by the building owner and as designed by the building architects and engineers.

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An independent, certified, commissioning authority under contract to the owner is the preferred contractual arrangement between a commissioning provider and building owner. A third party professional brings objectivity and practical experience to the project to ensure that the owner will truly get the building performance that he or she expects. ACG members must be independent.

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Although contractors may have the knowledge and capability to test the equipment they install, they may not be skilled at testing or diagnosing integration problems. In addition, some contend that it is difficult for contractors to objectively test and assess their own work, especially since repairing deficiencies found through commissioning may increase their costs.