The Constitution was adopted on September 17, 1787, by the Constitutional Convention in Philadelphia, Pennsylvania, and ratified by conventions in eleven States. It went into effect on March 4, 1789.
Since the Constitution was adopted, it has been amended twenty-seven times. The first ten of amendments (along with two others that were not ratified at the time) were proposed by Congress on September 25, 1789, and were ratified by the necessary three-fourths of the States on December 15, 1791. These first ten amendments are known as the Bill of Rights.
The Constitution is interpreted, supplemented, and implemented by a large body of constitutional law. The Constitution of the United States was the first constitution of its kind, and has influenced the constitutions of many other nations.