Delegates signed the United States Constitution at Independence Hall on September 17, 1787.
The signing concluded the Constitutional Convention in Philadelphia. Thirty-nine delegates endorsed the document that day, representing twelve states; Rhode Island had declined to send delegates to the convention. George Washington, who chaired the convention, signed along with other prominent delegates.
The Constitution created a federal framework with a legislature, executive, and judiciary, while also establishing relationships between the national government and the states. It did not become operative merely because delegates signed it. Article Seven sent the document to state conventions for ratification, requiring approval from nine states.
September 17 is now observed in the United States as Constitution Day and Citizenship Day. The date is separate from July 4, 1776, when Congress adopted the Declaration of Independence, and from June 21, 1788, when New Hampshire supplied the ninth ratification needed for the Constitution to take effect.