The United States Constitution received its signatures at Independence Hall on September 17, 1787.
That day marked the end of the Constitutional Convention’s work in Philadelphia. Thirty-nine delegates signed the document, which established a proposed federal government to replace the system operating under the Articles of Confederation. The convention had begun its formal sessions on May 25 and completed the document after months of debate.
Signing did not immediately make the Constitution effective. The document required ratification by conventions in at least nine states. New Hampshire became the ninth state to ratify on June 21, 1788, and the new federal government began operating in 1789.
September 17 is now observed in the United States as Constitution Day and Citizenship Day. It is sometimes confused with the ratification date or the date the new government began, but those were later milestones in the constitutional process.