Project commissioning is the process of assuring that all systems and components of a building or industrial plant are designed, installed, tested, operated, and maintained according to the operational requirements of the owner or final client. A commissioning process may be applied not only to new projects but also to existing units and systems subject to expansion, renovation or revamping. 
In practice, the commissioning process comprises the integrated application of a set of engineering techniques and procedures to check, inspect and test every operational component of the project, from individual functions, such as instruments and equipment, up to complex amalgamations such as modules, subsystems and systems.
Commissioning activities, in the broader sense, are applicable to all phases of the project, from the basic and detailed design, procurement, construction and assembly, until the final handover of the unit to the owner, including sometimes an assisted operation phase.
Commissioning of large civil and industrial projects (such as chemical and petrochemical plants, oil and gas platforms and pipelines, metallurgical plants, paper and cellulose plants, coal handling plants, thermoelectric and hydroelectric plants, buildings, bridges, highways and railroads) is a complex and sophisticated technical specialty, which may be considered as a specific and independent engineering discipline, as important as the more traditional ones (civil, naval, chemical, mechanical, electrical, electronic, instrumentation, automation and telecom).
Objective and impact
The main objective of commissioning is to effectively the safe and orderly handover of the unit from the constructor to the owner, guaranteeing its operability in terms of performance, reliability, safety and information traceability. Additionally, when executed in a planned and effective way, commissioning normally represents an essential factor for the fulfillment of schedule, costs, safety and quality requirements of the project. 
Commissioning management systems
For complex projects, the large volume and complexity of commissioning data, together with the need to guarantee adequate information traceability, normally leads to the use of powerful IT tools, known as commissioning management systems, to allow effective planning and monitoring of the commissioning activities.
- HORSLEY, D. Process Plant Commissioning, a User Guide, Institution of Chemical Engineering, 1998.
- FARES, F., MONTENEGRO, B., PRATES, A., Commissioning of Oil & Gas Projects – Current Status, Evolution and Trends. in: Rio Oil & Gas 2010, Rio de Janeiro, Brazil, set 2010.
- BENDIKSEN, T., YOUNG, G. Commissioning of Offshore Oil and Gas Projects: The Manager's Handbook, AuthorHouse Publishers, 2005.