The United States Constitution was signed on September 17, 1787.
The signing took place at the Pennsylvania State House in Philadelphia, after delegates had spent nearly four months debating the proposed framework. Thirty-nine delegates signed the document. George Washington signed as convention president, and Benjamin Franklin was among the delegates who supported the final agreement.
Signing did not immediately make the Constitution the operating law of the United States. The document still needed ratification by state conventions. It took effect after New Hampshire became the ninth state to ratify it on June 21, 1788, and the new federal government began operating in 1789.
Some delegates refused to sign, including George Mason, Edmund Randolph, and Elbridge Gerry, because they objected to aspects of the document. The Constitution's signing date is now observed in the United States as Constitution Day and Citizenship Day.