A war flag, also known as a military flag, battle flag, or standard, is a variant of a national flag for use by a countrys military forces when on land. The nautical equivalent of a war flag is a naval ensign. Under the strictest sense of the term, few countries today currently have proper war flags, most preferring to use instead their state flag or standard national flag for this purpose.

War flags are used in the armies of countries, although they are not always visible. They are used to build pride and morale, and represent the groups honor. In battle, flags served as a rallying point when a formation was broken. Troops gathered around the flag to regroup, attack, or retreat.

Military units have carried flags and colors for centuries. Colors and flags affirm group identity. They build pride and morale, and represent the groups honor. In battle, flags served as a rallying point when a formation was broken. Troops gathered around the flag to regroup, attack, or retreat. Flags marked specific individuals, locations, and functions such as hospitals and ambulances.

During the Civil War, a soldier who captured enemy colors or saved his units colors frequently was honored. In addition to receiving a medal of honor, a soldier was sometimes given a leave of absence. Soldiers who captured enemy colors were often mentioned in dispatches and received promotions.