Thirty-nine delegates signed the United States Constitution in Philadelphia in 1787.
The signing occurred on September 17, 1787, at the final session of the Constitutional Convention in Independence Hall. The delegates had met to address weaknesses in the Articles of Confederation but produced an entirely new framework for the federal government.
Twelve states sent delegations to the convention; Rhode Island declined to participate. Not every delegate who attended signed the final document. Three delegates refused, and others had already departed, leaving 39 signatures.
The Constitution created three branches of government and a bicameral Congress. It was submitted to the states for ratification, becoming effective after the ninth state approved it in June 1788. The federal government began operating under it in 1789.