The signing of the United States Constitution took place at Independence Hall in Philadelphia on September 17, 1787.
Independence Hall was then known as the Pennsylvania State House. It hosted the Constitutional Convention, where delegates debated how to replace the weak national government created by the Articles of Confederation.
Thirty-nine delegates signed the finished Constitution. They represented 12 states; Rhode Island declined to send delegates to the convention. George Washington presided over the meetings, while James Madison kept detailed notes that became a major source for historians.
The building had already played a central role in the revolutionary era. The Declaration of Independence was adopted there in 1776, although the Constitution was signed in the same building 11 years later. The Constitution did not immediately become law: it required ratification by conventions in at least nine states.