The oath was a pledge signed by 576 members out of 577 of France's Third Estate and a few members of the First Estate on June 20, 1789 in a tennis court near the Palace of Versailles.
The meeting hall of the Estates General had been locked accidentally, but the Third Estate thought that this was an invasion of their rights, and were very angry with the king. They stood in a nearby indoor tennis court. They made a solemn vow that they would not move until "the voice of the country was heard" and their requests were met. They were joined by the nobles and clergy.