Thirty-nine delegates signed the United States Constitution on September 17, 1787, at Independence Hall in Philadelphia. Their signatures endorsed the document produced by the Constitutional Convention.
The convention had met for four months, beginning in May, and originally intended to revise the Articles of Confederation. Instead, the delegates created an entirely new framework for the federal government.
Delegates from 12 states signed the Constitution; Rhode Island did not send delegates to the convention. Not every delegate who attended the convention approved the final document, so the number of signers was smaller than the total attendance.
The Constitution then went to the states for ratification. Article Seven required approval by conventions in nine states, and the document took effect after New Hampshire became the ninth state to ratify it in June 1788.