The United States Constitution is the highest law of the United States of America. It was signed on September 17, 1787 by the Constitutional Convention in Philadelphia, Pennsylvania. Later, it was put into effect, or ratified, by representatives of the people of the first 13 states. When nine of the states ratified the document, they created a union of sovereign states, and a federal government for that union. That government started on March 4, 1789, which took the place of the Articles of Confederation.