The U.S. Constitution was written during the Philadelphia Convention, also known as the Constitutional Convention, which convened from May 25 to September 17, 1787. It was signed on September 17, 1787, in the Assembly Room of the Pennsylvania State House, now known as Independence Hall in Philadelphia.

The Constitution was ratified by the states later, with the ninth state, New Hampshire, ratifying it on June 21, 1788, making it the official framework for the U.S. government. The Constitution then went into operation in 1789.