The Officer Comanding (OC) is the commander of a sub-unit or minor unit (smaller than battalion size) in British and Commonwealth military usage.

Normally an Officer Commanding is a company, squadron or battery commander (typically a Major). However, the commanders of independent units of smaller than company size, detachments and administrative organisations, such as schools or wings, may also be designated Officers Commanding.

The term Officer Commanding cannot be applied to any oficer who is given command of a minor unit. For example, a platoon commander whose platoon is part of a company would not be an Officer Commanding. The Officer Commanding with power over that platoon would be the company OC. Officer Commanding is an appointment that confers a level of additonal powers and responsibilites on the appointee.

Officers Commanding are generally given the same power and responsibilites as Commanding Officers of battalions and regiments. They are held responsible for the unit's properties and monies, can hear disciplinary charges against soldiers/sailors/airmen under their command, and can delegate these powers.