The Constitutional Convention signed the U.S. Constitution on September 17, 1787.
Delegates met in Philadelphia during the Constitutional Convention to replace the Articles of Confederation with a new framework for the federal government. After months of debate and compromise, 39 delegates signed the completed Constitution on September 17.
The signing did not immediately put the Constitution into effect. Ratification by nine states was required, and the new government began operating in 1789. George Washington, who presided over the convention, was among the signers; Benjamin Franklin was another prominent participant.
September 17 is now observed in the United States as Constitution Day and Citizenship Day. It is sometimes confused with December 7, 1787, when Delaware became the first state to ratify the Constitution. America250’s founding-era timeline therefore includes both the document’s signing and the later state-by-state ratification process.