The Declaration of Pillnitz on August 27, 1791, was a statement issued at the Castle of Pillnitz in Saxony by Emperor Leopold II and Frederick William II of Prussia. Calling on European powers to intervene, this declaration was intended to serve as a warning to the French revolutionaries not to infringe further on the rights of Louis XVI, and to allow his restoration to power. It helped begin the French Revolutionary Wars.

It said that Austria would go to war if and only if all the other major European powers would also go to war with France. Leopold worded it this way so he wouldn't have to go to war because he knew William Pitt, the Prime Minister of Great Britain, did not support war with France. Leopold merely issued this to satisfy the emigres in his nation calling for foreign interference. France misunderstood this document thinking Leopold actually was going to declare war, so the French listened to the voices of radicals such as Marat, who wanted war.