Article Seven of the United States Constitution required nine state ratifications for the Constitution to take effect.
The rule was a compromise between the need for broad approval and the practical difficulty of securing unanimous agreement among the thirteen states. Article Seven stated that ratification by conventions in nine states would be sufficient to establish the Constitution among the states ratifying it.
New Hampshire became the ninth state to ratify on June 21, 1788. That milestone placed the Constitution into effect, although several states had not yet approved it. Virginia and New York followed soon afterward, while North Carolina and Rhode Island waited until after the new federal government had begun operating.
The requirement was not the same as unanimous approval by all thirteen states. The Articles of Confederation had required the consent of every state for major changes, but the Constitution used a different ratification formula. This distinction helped the proposed government move forward despite continuing opposition in some states.