On 20 June 1789, the members of the French Third Estate took the Tennis Court Oath (French: Serment du Jeu de Paume) in the tennis court which had been built in 1686 for the use of the Versailles palace. Their vow "not to separate and to reassemble wherever necessary until the Constitution of the kingdom is established"[1] became a pivotal event in the French Revolution.

The Estates-General had been called to address the country's fiscal and agricultural crisis, but they had become bogged down in issues of representation immediately after convening in May 1789, particularly whether they would vote by order or by head (which would increase the power of the Third Estate, as they outnumbered the other two estates by a large margin). On 17 June, the Third Estate began to call themselves the National Assembly, led by Honoré Gabriel Riqueti, Comte de Mirabeau.

On the morning of 20 June, the deputies were shocked to discover that the chamber door was locked and guarded by soldiers. They immediately feared the worst and were anxious that a royal attack was imminent from King Louis XVI, so upon the suggestion of one of their members Joseph-Ignace Guillotin, the deputies congregated in a nearby indoor royal tennis court near the Palace of Versailles. There 576 of the 577 members from the Third Estate took the oath — the only person who did not join was Joseph Martin-Dauch from Castelnaudary, who would only execute decisions that were made by the monarch.