The Bill of Rights are the first ten amendments to the United States Constitution. They were introduced as a series of amendments in 1789 in the First United States Congress by James Madison. Ten of the amendments were ratified and became the Bill of Rights in 1791. These amendments limit the powers of the federal government, protecting the rights of all citizens, residents and visitors on United States territory. Among the enumerated rights these amendments guarantee are: the freedoms of speech, press, and religion; the right to keep and bear arms; the freedom of assembly; the freedom to petition; and the rights to be free of unreasonable search and seizure; cruel and unusual punishment; and compelled self-incrimination. The Bill of Rights also restricts Congress' power by prohibiting it from making any law respecting establishment of religion and by prohibiting the federal government from depriving any person of life, liberty, or property without due process of law. In criminal cases, it requires indictment by grand jury for any capital or "infamous crime," guarantees a speedy public trial with an impartial and local jury, and prohibits double jeopardy. In addition, the Bill of Rights states that "the enumeration in the Constitution, of certain rights, shall not be construed to deny or disparage others retained by the people," and reserves all powers not granted to the federal government to the citizenry or states.

These amendments came into effect on December 15, 1791, when ratified by three-fourths of the states. Most were applied to the states by a series of decisions applying the due process clause of the Fourteenth Amendment, which was adopted after the American Civil War.

Initially drafted by James Madison in 1789, the Bill of Rights was written at a time when ideological conflict between Federalists and anti-Federalists, dating from the Philadelphia Convention in 1787, threatened the Constitution's ratification. The Bill was influenced by George Mason's 1776 Virginia Declaration of Rights, the 1689 English Bill of Rights, works of the Age of Enlightenment pertaining to natural rights, and earlier English political documents such as Magna Carta (1215). The Bill was largely a response to the Constitution's influential opponents, including prominent Founding Fathers, who argued that it failed to protect the basic principles of human liberty.

The Bill of Rights plays a central role in American law and government, and remains a fundamental symbol of the freedoms and culture of the nation. One of the original fourteen copies of the Bill of Rights is on public display at the National Archives in Washington, D.C.

The original document proposed by Congress to the states actually contained twelve "Articles" of proposed amendment. However, only the third through twelfth articles, corresponding to what became the First through Tenth Amendments to the Constitution, were ratified by the required number of states by 1791. The first Article, dealing with the number and apportionment of members of the House of Representatives, never became part of the Constitution. The second Article, limiting the ability of Congress to increase the salaries of its members, was ratified two centuries later as the 27th Amendment. The term "Bill of Rights" has traditionally meant only the ten amendments that became part of the Constitution in 1791, and not the first two, which dealt with Congress itself rather than the rights of the people. That traditional usage has continued even since the ratification of the 27th Amendment.