The United States Constitution is the supreme law of the United States of America. Drafted during the Constitutional Convention in Philadelphia, Pennsylvania, and signed on 17 September 1787, it established the framework of the federal government, defined the separation of powers among its three branches, and set limits on governmental authority. It was ratified by the requisite nine states on 21 June 1788, when New Hampshire became the ninth state to approve it, and took operational effect on 4 March 1789. The Constitution has been amended twenty-seven times; the first ten amendments, ratified on 15 December 1791, are collectively known as the Bill of Rights. It is the oldest written national constitution still in active use.

The Constitution consists of a preamble, seven original articles, and twenty-seven amendments. Article I establishes the Congress, a bicameral legislature composed of the Senate and the House of Representatives, and enumerates its legislative powers. Article II establishes the executive branch and the office of the President. Article III establishes the federal judiciary, including the Supreme Court, though it leaves the structure of lower courts to congressional discretion. Articles IV through VII address relations among the states, the amendment process, federal supremacy, and ratification. The Three-Fifths Clause (Article I, Section 2), which counted three-fifths of the enslaved population for purposes of apportionment, was rendered inoperative by the Fourteenth Amendment (1868).

Constitutional interpretation has been a central and ongoing feature of American legal and political life. The principal divide is between originalism, which holds that the Constitution should be interpreted according to its original public meaning or the framers' intent, and living constitutionalism, which holds that its meaning should evolve with changing social circumstances. These are not the only approaches; textualism, structuralism, and moral readings of the Constitution each have scholarly proponents. The Supreme Court has final authority over constitutional interpretation in federal matters, though the legitimacy and scope of that authority are themselves subjects of debate. See United States Constitution - Debate for competing arguments.

The Constitution emerged from dissatisfaction with the Articles of Confederation, which had governed the United States since 1781 and were widely regarded as inadequate to sustain a functional national government. The Constitutional Convention convened in May 1787, with delegates from twelve of the thirteen states; Rhode Island did not participate. Ratification was contentious, with Anti-Federalists warning against the concentration of federal power and Federalists, most prominently in The Federalist Papers, arguing for the necessity of a stronger union. The promise of a Bill of Rights was instrumental in securing ratification in several states. For a fuller account, see United States Constitution - History.

The Constitution has been amended twenty-seven times. Significant amendments include the Bill of Rights (Amendments I-X, 1791), which protects freedoms of speech, religion, and the press, among others; the Thirteenth Amendment (1865), abolishing slavery; the Fourteenth Amendment (1868), establishing birthright citizenship and equal protection; the Fifteenth Amendment (1870), prohibiting denial of the vote on account of race; the Nineteenth Amendment (1920), extending the vote to women; and the Twenty-Seventh Amendment (1992), restricting congressional pay changes. The amendment process requires approval by two-thirds of both houses of Congress and ratification by three-fourths of the states, a deliberately high threshold that has been a subject of both praise and criticism.

There is broad scholarly consensus that the Constitution, as written, established a federal republic with separated powers and individual rights protections, and that it has functioned as the operative supreme law of the United States since 1789. Interpretive questions - regarding the scope of enumerated powers, the meaning of specific clauses, and the proper method of constitutional interpretation - remain actively contested in both law and political theory. See United States Constitution - Legal Consensus for scholarly areas of agreement.

• Originalism - The Constitution's meaning is fixed at the time of ratification and should be applied according to its original public meaning.
• Living Constitutionalism - The Constitution's meaning adapts over time and should be interpreted in light of evolving social standards and conditions.
• Popular Constitutionalism - Constitutional meaning is not solely the province of courts but is shaped by democratic politics and popular engagement.
• Departmentalism - Each branch of the federal government has independent authority to interpret the Constitution within its own sphere.
• Abolitionist and Critical Critique - Some scholars and activists have argued that the Constitution's original text was structured to protect slavery and that this legacy shapes its ongoing interpretation.

• United States Constitution - History
• United States Constitution - Debate
• United States Constitution - Legal Consensus
• Bill of Rights
• United States Supreme Court
• Constitutional Originalism
• Living Constitutionalism
• Articles of Confederation
• The Federalist Papers
• Fourteenth Amendment
• Separation of Powers

1. U.S. Const. (1787). National Archives. https://www.archives.gov/founding-docs/constitution
2. Pauline Maier, Ratification: The People Debate the Constitution, 1787-1788 (Simon & Schuster, 2010).
3. Alexander Hamilton, James Madison, and John Jay, The Federalist Papers (1787-1788).
4. Akhil Reed Amar, America's Constitution: A Biography (Random House, 2005).
5. Antonin Scalia, A Matter of Interpretation: Federal Courts and the Law (Princeton University Press, 1997).
6. David A. Strauss, The Living Constitution (Oxford University Press, 2010).
7. Don E. Fehrenbacher, The Slaveholding Republic: An Account of the United States Government's Relations to Slavery (Oxford University Press, 2001).