In modern use, the order of battle of an armed force participating in a military operation or campaign shows the hierarchical organization, command structure, strength, disposition of personnel, and equipment of units and formations of the armed force. Various abbreviations are in use, including OOB, O/B, or OB, while ORBAT remains the most common in the United Kingdom. An order of battle is distinct from a table of organisation, which is the intended composition of a given unit or formation according to the military doctrine of its armed force. Historically, an order of battle was the order in which troops were positioned relative to the position of the army commander or the chronological order in which ships were deployed in naval situations.

As combat operations develop during a campaign, orders of battle may be revised and altered in response to the military needs and challenges. Also the known details of an order of battle may change during the course of executing the commanders' after action reports and/or other accounting methods (e.g. despatches) as combat assessment is conducted.