The U.S. Constitution took effect on March 4, 1789, beginning the new federal government.
The Constitution replaced the Articles of Confederation, the United States’ first governing framework. After nine states ratified it, the document became eligible to establish the new government, but its operating date was set for March 4, 1789.
The first Congress convened in New York City on that date. George Washington was later inaugurated as the first president on April 30, 1789, also in New York City. These dates are sometimes confused because the Constitution was signed on September 17, 1787, and ratified by the required ninth state on June 21, 1788.
The Constitution established the three branches of the federal government: Congress, the presidency, and the federal judiciary. It also created a stronger union than the Articles of Confederation had provided. The document remains the supreme law of the United States and has been amended 27 times.