The Tennis Court Oath (serment du jeu de paume) was a pledge signed by 577 members of France's Third Estate on June 20, 1789. It was an early decisive step in starting the French Revolution.

King Louis XVI had locked the deputies of the Third Estate out of their meeting hall, Menus Plaisirs; they met instead in a nearby indoor real tennis court, where they adopted a pledge to continue to meet until a constitution had been written. 577 men signed the oath, with only one delegate refusing. This was a revolutionary act, and an assertion that political authority derived from the people and their representatives rather than from the monarch.

One week later Louis XVI called for a meeting of the Estates General for the purpose of writing a constitution for France.

The Tennis Court Oath is often considered the moment of the birth of the French Revolution.