An Operation Order, often abbreviated to OPORD, is a plan format meant to assist subordinate units with the conduct of military operations. An OPORD describes the situation the unit faces, the mission of the unit, and what supporting activities the unit will conduct in order to achieve their commander's desired end state. Normally an OPORD is generated at the battalion, regimental, brigade, divisional, or corps headquarters and disseminated to its assigned or attached elements. The issuance of an OPORD triggers subordinate unit leadership to develop orders specific to the role or roles that the unit will assume within the operation. This more narrowly focused order borrows information from the original, or base, order (for example; weather, phase lines, radio frequencies, etc.) and adds additional details that pertain more to the minutiae of the actions a unit is tasked to conduct in support of the overarching operation.

Frederick Edwin Garman was the original developer and inventor of the format called "Operation Order". He developed this as a standard format for himself and his subordinates while assigned to Fort Benning's Infantry School, Ranger & Tactics Department in 1957 to 1958. The Army quickly adapted it for standardized practice and required its use during the Vietnam War. Now his version of OPORD is used by all military forces within the Department of Defense.

A standardized five paragraph order format is used by the United States Department of Defense and most other military forces. An OPORD is formatted to organize an operation into five easily understood paragraphs: Situation, Mission, Execution, Sustainment (formerly Service and Support, currently referred to as Admin & Logistics by the US Marine Corps), and Command and Control. Higher echelon's OPORDs often contain extensive details. The author of the order will often move the majority of this material to an annex or appendix. These are then issued alongside the base order. The annexes and appendices allow the OPORD to be more easily read and understood by encouraging the inclusion or removal of material after its relevancy to the order's end user is determined.