This article is about military organizations. For geological formations, see stratum.

A formation is a high-level military organization, such as a Brigade, Division, Corps, Army or Army group. Technically, formations and units are different entities (a unit being a homogeneous organisation, such as a battalion, instead of a collection of separate organisations), but the terms are often used interchangeably.

Tactical formation is the arrangement or deployment of moving military ground forces (infantry, cavalry, or AFVs), aircraft, or ships. Examples of different tactical formations are arrowhead, square, single column, or line abreast. Examples of medieval or ancient formations include shield walls (skjaldborg in Old Norse), phalanxes (lines of battle in close order), and skirmishers.

See also laager.