A field officer, field-grade officer, or senior officer is an army, Marine, or air force commissioned officer senior in rank to a company officer but junior to a general officer. In most armies this corresponds to the ranks of major, lieutenant colonel and colonel, or their equivalents. Some countries also include brigadier in the definition.
Historically, a regiment or battalion's field officers made up its command element.
In the Canadian Armed Forces, the equivalent of field officers are senior officers (French: Officiers supérieurs); they include the army and air force ranks of Major, Lieutenant-Colonel, and Colonel, and the naval ranks of Lieutenant-Commander, Commander, and Captain.