The United States Constitution was signed at Independence Hall on September 17, 1787.
The signing concluded the Constitutional Convention in Philadelphia, which had met from May 25 through September 17. The convention was called to revise the Articles of Confederation but instead produced an entirely new framework for the federal government.
Thirty-nine delegates signed the document. Fifty-five delegates attended the convention at some point, while 74 had originally been selected. Rhode Island did not send delegates, and three delegates who remained at the convention—George Mason, Edmund Randolph, and Elbridge Gerry—declined to sign.
September 17 is now observed in the United States as Constitution Day and Citizenship Day. The Constitution did not take effect immediately: it required ratification by nine states, which occurred when New Hampshire ratified it on June 21, 1788. The new federal government began operating in 1789.