The Constitutional Convention signed the United States Constitution on September 17, 1787.
Delegates met in Philadelphia to revise the Articles of Confederation, but they ultimately produced an entirely new framework for the federal government. The convention began in May and completed its work in September. Thirty-nine delegates signed the document on September 17.
The Constitution did not become operative immediately upon signing. It required ratification by nine states, which occurred when New Hampshire ratified it on June 21, 1788. The new government began in 1789, with George Washington inaugurated as president.
September 17 is observed in the United States as Constitution Day and Citizenship Day. The date is distinct from July 4, 1776, when Congress adopted the Declaration of Independence. America250 focuses on the 1776 anniversary, but the Constitution is an essential later chapter in the nation’s founding story.