The members of the Constitutional Convention approved the new Constitution on this day in 1787. The Constitution then went to the old Confederation Congress, which approved the submission of the Constitution to conventions of the States.
The Constitution took effect on June 21, 1788, when it was ratified by a ninth State (New Hampshire), though it bound only the nine States that had thus far ratified it. The other four States followed suit, but the Constitution was not ratified by — and did not become binding on — all thirteen States until Rhode Island joined the Union on May 29, 1790. By then, more than a year had passed since the first Congress of the United States had assembled and George Washington had been inaugurated.
In honor of the original Constitution — which has been shredded by generations of legislative, executive, and judicial malfeasance — I refer you to these posts: