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The Constitution of the United States is the supreme law of the United States of America. The Constitution originally consisted of seven Articles. The first three Articles embody the doctrine of the separation of powers, whereby the federal government is divided into three branches: the legislature, consisting of the bicameral Congress; the executive, consisting of the President; and the judiciary, consisting of the Supreme Court and other federal courts. The fourth and sixth Articles frame the doctrine of federalism, describing the relationship between State and State, and between the several States and the federal government. The fifth Article provides the procedure for amending the Constitution. The seventh Article provides the procedure for ratifying the Constitution.

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 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.