The French ruse de guerre, sometimes literally translated as ruse of war, is a non-uniform term; generally what is understood by "ruse of war" can be separated into two groups. The first classifies the phrase purely as an act of military deception against one's opponent; the second emphasizes acts against one's opponent by creative, clever, unorthodox means, sometimes involving force multipliers or superior knowledge. The term stratagem, from Ancient Greek strategema (στρατήγημα, 'act of generalship'), is also used in this sense.

Ruses de guerre are described from ancient to modern times, both in semi-mythical accounts such as the story of the Trojan Horse in Virgil's Aeneid, and in well-documented events such as the flying of the American flag by the British ocean liner RMS Lusitania in 1915 (whilst the United States was a neutral country) to deter attack by German submarines; they also feature in fiction.

The term ruse de guerre is given legal meaning within the rules of war. Good faith is required, but at least 17 different types of ruse, including ambushes, false radio messages, the use of spies and the use of dummy guns, are considered legitimate as long as they do not involve treachery or perfidy. Landmines and similar traps can be considered perfidious under the rules in certain circumstances. Explicitly prohibited ruses under article 23 of the Hague Convention of 1907 include improper use of a flag of truce or the military insignia of the enemy.