Delegates signed the United States Constitution on September 17, 1787.
The signing took place at the Pennsylvania State House in Philadelphia, now known as Independence Hall, after the Constitutional Convention completed its work. Thirty-nine delegates signed the document, while several delegates who attended the convention declined to sign or were absent.
The signing did not immediately make the Constitution the nation’s operating framework. Article Seven required ratification by nine states, and New Hampshire supplied the decisive ninth ratification on June 21, 1788. 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 distinct from July 4, 1776, the date the Declaration of Independence was adopted, and from March 4, 1789, when the Constitution’s government formally began.