Constitution of the United States of America, the fundamental law of the U.S. federal system of government and a landmark document of the Western world. The oldest written national constitution in use, the Constitution defines the principal organs of government and their jurisdictions and the basic rights of citizens.
The Constitution was written during the summer of 1787 in Philadelphia, Pennsylvania, by 55 delegates to a Constitutional Convention that was called ostensibly to amend the Articles of Confederation (1781–89), the country’s first written constitution. The Constitution was the product of political compromise after long and often rancorous debates over issues such as states’ rights, representation, and slavery. Delegates from small and large states disagreed over whether the number of representatives in the new federal legislature should be the same for each state—as was the case under the Articles of Confederation—or different depending on a state’s population (see New Jersey Plan and Virginia Plan). In addition, some delegates from Northern states sought to abolish slavery or, failing that, to make representation dependent on the size of a state’s free population. At the same time, some Southern delegates threatened to abandon the convention if their demands to keep slavery and the slave trade legal and to count slaves for representation purposes were not met. Eventually the framers resolved their disputes by adopting a proposal put forward by the Connecticut delegation. The Great Compromise, as it came to be known, created a bicameral legislature with a Senate, in which all states would be equally represented, and a House of Representatives, in which representation would be apportioned on the basis of a state’s free population plus three-fifths of its enslaved population. (The inclusion of the enslaved population was known separately as the three-fifths compromise.) A further compromise on slavery prohibited Congress from banning the importation of enslaved people until 1808 (Article I, Section 9). After all the disagreements were bridged, the new Constitution was signed by 39 delegates on September 17, 1787, and it was submitted for ratification to the 13 states on September 28.
In 1787–88, in an effort to persuade New York to ratify the Constitution, Alexander Hamilton, John Jay, and James Madison published a series of essays on the Constitution and republican government in New York newspapers. Their work, written under the pseudonym “Publius” and collected and published in book form as The Federalist (1788), became a classic exposition and defense of the Constitution. In June 1788, after the Constitution had been ratified by nine states (as required by Article VII), Congress set March 4, 1789, as the date for the new government to commence proceedings (the first elections under the Constitution were held late in 1788). Because ratification in many states was contingent on the promised addition of a Bill of Rights, Congress proposed 12 amendments in September 1789; 10 were ratified by the states, and their adoption was certified on December 15, 1791. (One of the original 12 proposed amendments, which prohibited midterm changes in compensation for members of Congress, was ratified in 1992 as the Twenty-seventh Amendment. The last one, concerning the ratio of citizens per member of the House of Representatives, has never been adopted.)
The authors of the Constitution were heavily influenced by the country’s experience under the Articles of Confederation, which had attempted to retain as much independence and sovereignty for the states as possible and to assign to the central government only those nationally important functions that the states could not handle individually. But the events of the years 1781 to 1787, including the national government’s inability to act during Shays’s Rebellion (1786–87) in Massachusetts, showed that the Articles were unworkable because they deprived the national government of many essential powers, including direct taxation and the ability to regulate interstate commerce. It was hoped that the new Constitution would remedy this problem.
The framers of the Constitution were especially concerned with limiting the power of government and securing the liberty of citizens. The doctrine of legislative, executive, and judicial separation of powers, the checks and balances of each branch against the others, and the explicit guarantees of individual liberty were all designed to strike a balance between authority and liberty—the central purpose of American constitutional law.
Provisions
The Constitution concisely organizes the country’s basic political institutions. The main text comprises seven articles.
n Article I vests all legislative powers in the Congress—the House of Representatives and the Senate. The Great Compromise stipulated that representation in the House would be based on population, and each state is entitled to two senators. Members of the House serve terms of two years, senators terms of six. Among the powers delegated to Congress are the right to levy taxes, borrow money, regulate interstate commerce, provide for military forces, declare war, and determine member seating and rules of procedure. The House initiates impeachment proceedings, and the Senate adjudicates them.
n Article II vests executive power in the office of the presidency of the United States. The president, selected by an electoral college to serve a four-year term, is given responsibilities common to chief executives, including serving as commander in chief of the armed forces, negotiating treaties (two-thirds of the Senate must concur), and granting pardons. The president’s vast appointment powers, which include members of the federal judiciary and the cabinet, are subject to the “advice and consent” (majority approval) of the Senate (Article II, Section 2). Originally presidents were eligible for continual reelection, but the Twenty-second Amendment (1951) later prohibited any person from being elected president more than twice. Although the formal powers of the president are constitutionally quite limited and vague in comparison with those of the Congress, a variety of historical and technological factors—such as the centralization of power in the executive branch during war and the advent of television—have increased the informal responsibilities of the office extensively to embrace other aspects of political leadership, including proposing legislation to Congress.

n Article III places judicial power in the hands of the courts. The Constitution is interpreted by the courts, and the Supreme Court of the United States is the final court of appeal from the state and lower federal courts. The power of American courts to rule on the constitutionality of laws, known as judicial review, is held by few other courts in the world and is not explicitly granted in the Constitution. The principle of judicial review was first asserted by Supreme Court Chief Justice John Marshall in Marbury v. Madison (1803), when the court ruled that it had the authority to void national or state laws.
Beyond the body of judicial rulings interpreting it, the Constitution acquires meaning in a broader sense at the hands of all who use it. Congress on innumerable occasions has given new scope to the document through statutes, such as those creating executive departments, the federal courts, territories, and states; controlling succession to the presidency; and setting up the executive budget system. The chief executive also has contributed to constitutional interpretation, as in the development of the executive agreement as an instrument of foreign policy. Practices outside the letter of the Constitution based on custom and usage are often recognized as constitutional elements; they include the system of political parties, presidential nomination procedures, and the conduct of election campaigns. The presidential cabinet is largely a constitutional “convention” based on custom, and the actual operation of the electoral college system is also a convention.
n Article IV deals, in part, with relations between the states and privileges of the citizens of the states. These provisions include the full faith and credit clause, which requires states to recognize the official acts and judicial proceedings of other states; the requirement that each state provide citizens from other states with all the privileges and immunities afforded the citizens of that state; and the guarantee of a republican form of government for each state.
n Article V stipulates the procedures for amending the Constitution. Amendments may be proposed by a two-thirds vote of both houses of Congress or by a convention called by Congress on the application of the legislatures of two-thirds of the states. Proposed amendments must be ratified by three-fourths of the state legislatures or by conventions in as many states, depending on the decision of Congress. All subsequent amendments have been proposed by Congress, and all but one—the Twenty-first Amendment (1933), which repealed prohibition (the Eighteenth Amendment [1919])—have been ratified by state legislatures.
n Article VI, which prohibits religious tests for officeholders, also deals with public debts and the supremacy of the Constitution, citing the document as “the supreme Law of the Land;…any Thing in the Constitution or Laws of any State to the Contrary notwithstanding.” Article VII stipulated that the Constitution would become operational after being ratified by nine states.
The national government has only those constitutional powers that are delegated to it either expressly or by implication; the states, unless otherwise restricted, possess all the remaining powers (Tenth Amendment). Thus, national powers are enumerated (Article I, Section 8, paragraphs 1–17), and state powers are not. The state powers are often called residual, or reserved, powers. The elastic, or necessary and proper, clause (Article I, Section 8, paragraph 18) states that Congress shall have the authority “To make all Laws which shall be necessary and proper for carrying into Execution” the various powers vested in the national government. Thus, it follows that, in addition to the delegated powers, Congress possesses implied powers, a proposition established by Chief Justice Marshall in McCulloch v. Maryland (1819). The issue of national versus state power was not fully resolved by this decision, however, and many political battles in American history—including debates on nullification, slavery, racial segregation, and abortion—often have been disputes over constitutional interpretations of implied and residual powers.
Competing concepts of federal supremacy and states’ rights were brought into sharp relief in questions about commercial regulation. The commerce clause simply authorized Congress “To regulate Commerce with foreign Nations, and among the several States, and with the Indian Tribes.” Particularly since a series of decisions in 1937, the court has interpreted Congress’s regulatory power broadly under the commerce clause as new methods of interstate transportation and communication have come into use. States may not regulate any aspect of interstate commerce that Congress has preempted.
Civil liberties and the Bill of Rights
The federal government is obliged by many constitutional provisions to respect the individual citizen’s basic rights. Some civil liberties were specified in the original document, notably in the provisions guaranteeing the writ of habeas corpus and trial by jury in criminal cases (Article III, Section 2) and forbidding bills of attainder and ex post facto laws (Article I, Section 9). But the most significant limitations to government’s power over the individual were added in 1791 in the Bill of Rights. The Constitution’s First Amendment guarantees the rights of conscience, such as freedom of religion, speech, and the press, and the right of peaceful assembly and petition. Other guarantees in the Bill of Rights require fair procedures for persons accused of a crime—such as protection against unreasonable search and seizure, compulsory self-incrimination, double jeopardy, and excessive bail—and guarantees of a speedy and public trial by a local, impartial jury before an impartial judge and representation by counsel. Rights of private property are also guaranteed. Although the Bill of Rights is a broad expression of individual civil liberties, the ambiguous wording of many of its provisions—such as the Second Amendment’s right “to keep and bear arms” and the Eighth Amendment’s prohibition of “cruel and unusual punishments”—has been a source of constitutional controversy and intense political debate. Further, the rights guaranteed are not absolute, and there has been considerable disagreement about the extent to which they limit governmental authority. The Bill of Rights originally protected citizens only from the national government. For example, although the Constitution prohibited the establishment of an official religion at the national level, the official state-supported religion of Massachusetts was Congregationalism until 1833. Thus, individual citizens had to look to state constitutions for protection of their rights against state governments.
The Fourteenth Amendment
After the American Civil War, three new constitutional amendments were adopted: the Thirteenth (1865), which abolished slavery; the Fourteenth (1868), which granted citizenship to those who had been enslaved; and the Fifteenth (1870), which guaranteed formerly enslaved men the right to vote. The Fourteenth Amendment placed an important federal limitation on the states by forbidding them to deny to any person “life, liberty, or property, without due process of law” and guaranteeing every person within a state’s jurisdiction “the equal protection of its laws.” Later interpretations by the Supreme Court in the 20th century gave these two clauses added significance. In Gitlow v. New York (1925), the due process clause was interpreted by the Supreme Court to broaden the applicability of the Bill of Rights’ protection of speech to the states, holding both levels of government to the same constitutional standard. During subsequent decades, the Supreme Court selectively applied the due process clause to protect from state infringement other rights and liberties guaranteed in the Bill of Rights, a process known as “selective incorporation.” Those rights and liberties included freedom of religion and of the press and the right to a fair trial, including the right to an impartial judge and to the assistance of counsel. Most controversial were the Supreme Court’s use of the due process clause to ground an implicit right of privacy in Roe v. Wade (1973), which led to the nationwide legalization of abortion, and its selective incorporation of the Second Amendment’s right to “keep and bear Arms” in McDonald v. Chicago (2010).
The Supreme Court applied the equal protection clause of the Fourteenth Amendment in its landmark decision in Brown v. Board of Education of Topeka (1954), in which it ruled that racial segregation in public schools was unconstitutional. In the 1960s and ’70s the equal protection clause was used by the Supreme Court to extend protections to other areas, including zoning laws, voting rights, and gender discrimination. The broad interpretation of this clause has also caused considerable controversy.
The Constitution as a living document
Twenty-seven amendments have been added to the Constitution since 1789. In addition to those mentioned above, other far-reaching amendments include the Sixteenth (1913), which allowed Congress to impose an income tax; the Seventeenth (1913), which provided for direct election of senators; the Nineteenth (1920), which mandated women’s suffrage; and the Twenty-sixth (1971), which granted suffrage to citizens 18 years of age and older.In more than two centuries of operation, the United States Constitution has proved itself a dynamic document. It has served as a model for other countries, its provisions being widely imitated in national constitutions throughout the world. Although the Constitution’s brevity and ambiguity have sometimes led to serious disputes about its meaning, they also have made it adaptable to changing historical circumstances and ensured its relevance in ages far removed from the one in which it was written.