Delegates signed the U.S. Constitution on September 17, 1787, at the Pennsylvania State House, now called Independence Hall, in Philadelphia.
The Constitutional Convention had met for four months to create a new framework of government. Thirty-nine delegates from twelve states signed the final document. Rhode Island did not send delegates to the convention, and several delegates who attended declined to sign.
George Washington, who presided over the convention, signed first. The document then went to the states for ratification. Article Seven required approval by conventions in nine states, rather than unanimous approval by all thirteen.
September 17 is now observed as Constitution Day and Citizenship Day in the United States. The date is often mixed up with June 21, 1788, when New Hampshire became the ninth state to ratify, or March 4, 1789, when the new federal government began operating under the Constitution.