The United States Constitution has served as the supreme law of the United States since taking effect in 1789. The document was written at the 1787 Philadelphia Convention and was ratified through a series of state conventions held in 1787 and 1788. Since 1789, the Constitution has been amended twenty-seven times; particularly important amendments include the ten amendments of the United States Bill of Rights, the three Reconstruction Amendments, and the Nineteenth Amendment.
The Constitution grew out of efforts to reform the Articles of Confederation, an earlier constitution which provided for a loose alliance of states with a weak central government.