A Field Force in British and Indian Army military parlance is a combined arms land force operating under actual or assumed combat circumstances usually for the length of a specific military campaign. It is used by other nations, but can have a different meaning.
United Kingdom Use 
A Field Force would be created from the various units in an area of military operations and be named for the geographical area. Examples are-
- Kurram Field Force, 1878
- Peshawar Valley Field Force, 1878
- Kabul Field Force, 1879-1880
- Kabul-Kandahar Field Force, 1880
- Natal Field Force, 1881
- Zhob Field Force, 1890
- Mashonaland Field Force, 1896
- Malakand Field Force, 1896
- Tirah Field Force, 1897
- Yukon Field Force, 1898
- Royal West African Frontier Force, 1900
Australian Use 
In Australia a Field Force comprises the units required to meet operational commitments.
United States Use 
In the United States, during the Vietnam War the term came to stand for a Corps-sized organization with other functions and responsibilities. To avoid confusion with the Corps designations used by the Army of the Republic of Vietnam and to allow for a flexible organization, MACV and General William Westmoreland developed the "Field Force" such as I Field Force and II Field Force. Unlike an Army Corps, which had a size and structure fixed by Army doctrine, the Field Force could expand as needed and had other functions such as liaison with South Vietnamese and Civil Affairs functions and was flexible enough to have many subordinate units assigned to it.
Police field forces 
In counter insurgency type campaigns, select and specially trained units of police armed and equipped as light infantry have been designated as police field forces who perform paramilitary type patrols and ambushes whilst retaining their police powers in areas that were highly dangerous.
Examples of these are:
- Royal Malaysian Police Police Field Force/General Operations Forces (Malayan Emergency)
- Kenya Police General Service Unit (Mau Mau Uprising)
- Tanzania Police Police Field Force (Zanzibar Revolution)
- Gambia Police Field Force
- Republic of Vietnam National Police Field Force (Vietnam War)
- British South Africa Police Support Unit (Rhodesian Bush War)
- Royal Solomon Islands Police Force Police Field Force
- Sri Lanka Special Task Force (Sri Lankan Civil War)
- Namibia Special Field Force
- p.88 Dupuy, Trevor N., Johnson, Curt and Hayes, Grace P. Dictionary of Military Terms: A Guide to the Language of Warfare and Military Institutions 1986 The H.W. Wilson Company
- Eckhard, George S. Vietnam Studies: Command and Control 1950-1969. Washington, DC: Department of the Army, 1991 p. 53. Online http://www.history.army.mil/books/Vietnam/Comm-Control/index.htm
- p.Davies, Bruce & McKay, Gary The Men Who Persevered:The AATTV 2005 Bruce & Unwin