The Gleiwitz incident was a false flag attack on the radio station Sender Gleiwitz in Gleiwitz staged by Nazi Germany on the night of 31 August 1939. Along with some two dozen similar incidents, the attack was manufactured by Germany as a casus belli to justify the invasion of Poland. Prior to the invasion, Adolf Hitler gave a radio address condemning the acts and announcing German plans to attack Poland, which began the next morning. Despite the German government using the attack as a justification to go to war with Poland, the Gleiwitz assailants were not Polish but were German SS officers wearing Polish uniforms.

A false flag operation is an act committed with the intent of disguising the actual source of responsibility and pinning blame on another party. The term "false flag" originated in the 16th century as an expression meaning an intentional misrepresentation of someone's allegiance. The term was famously used to describe a ruse in naval warfare whereby a vessel flew the flag of a neutral or enemy country in order to hide its true identity. The tactic was originally used by pirates and privateers to deceive other ships into allowing them to move closer before attacking them. It later was deemed an acceptable practice during naval warfare according to international maritime laws, provided the attacking vessel displayed its true flag once an attack had begun.