The Constitution organizes concisely the basic U.S. political institutions. The main text comprises seven articles.

Article I vests all legislative powers in the Congress -- the House of Representatives and the Senate. Among those powers 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. (see also Index: Representatives, House of)

Article II vests executive power in the president. The president's formal responsibilities include those of chief executive, commander in chief of the armed forces, and treaty maker (two-thirds of the Senate must concur). The powers of appointment of the president are vast but are subject to the "advice and consent" (majority approval) of the Senate (Article II, section 2). The informal responsibilities of the president have grown to embrace political leadership, including proposing legislation to Congress.

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 U.S. courts to rule on the constitutionality of laws is known as judicial review. Few courts in the world have that extraordinary power, which is not explicitly mentioned in the Constitution. The definitive assertion of judicial review was made by Chief Justice John Marshall in Marbury v. Madison (1803; q.v.).

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,

Supreme Court of the United States, final court of appeal and final expositor of the U.S. Constitution. Within the framework of litigation, the Supreme Court marks the boundaries of authority between state and nation, state and state, and government and citizen.

Article IV deals, in part, with relations among the states and privileges of the citizens of the states,

Article V with amendment procedure.

Article VI with public debts and the supremacy of the Constitution.

Article VII gives ratification terms. Under the Constitution, the national government has only those constitutional powers that are delegated to it; the states, unless otherwise restricted, possess all the remaining powers of government (Tenth Amendment). Thus, national powers are enumerated, state powers are not. The state powers are often called residual powers. (see also Index: state government)

Although the national government is limited to its enumerated powers, Article VI cites the Constitution as "the supreme Law of the Land; . . . any Thing in the Constitution or Laws of any State to the Contrary notwithstanding." The "elastic" clause of the Constitution (Article I, section 8) 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 by the Constitution. It follows that, in addition to the specified powers, Congress possesses implied powers, a proposition definitively established by Chief Justice Marshall in McCulloch v. Maryland (1819; q.v.).

Early in U.S. history, competing concepts of federal supremacy and states' rights were brought into sharp focus in questions about commercial regulation. The commerce clause (Article I, section 8) simply authorizes Congress "To regulate Commerce with foreign Nations, and among the several States, and with the Indian Tribes." From Gibbons v. Ogden (1824) on, the Supreme Court has broadly interpreted Congress' regulatory power 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.

The federal government is obliged by many constitutional provisions to respect an individual citizen's basic rights. Some civil rights were specified in the original document, notably in the provisions guaranteeing the writ of habeas corpus and forbidding bills of attainder and ex post facto laws (Article I, section 9). It also guaranteed trial by jury in criminal cases (Article III, section 2). But the most significant limitations to government's power over the individual were added in 1791 in the Bill of Rights. The 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 include fair procedure for persons accused of crime, such as protection against unreasonable search and seizure and against compulsory self-incrimination and excessive bail, 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. (see also Index: freedom of speech, freedom of the press)

For protection of such rights against state action, the citizen originally had to look to each state constitution. An important new federal limitation on the states was added to the Constitution of the United States with the ratification, in 1868, of the Fourteenth Amendment. It forbids any state to deny to any person "life, liberty, or property, without due process of law" or to "deny to any person within its jurisdiction the equal protection of its laws." Interpretation by the Supreme Court gave these two clauses increased meaning.

The due process clause of the Fourteenth Amendment has been held to include the liberties of religion, speech, and press that the First Amendment protects against violation by the federal government. Similarly, certain guarantees of a fair trial, such as the defendant's right to an impartial judge and the assistance of counsel, have also been judicially absorbed into the Fourteenth Amendment.

The other great limitation on the states in the Fourteenth Amendment--that no state shall deny the equal protection of its laws--has a long and important history in U.S. constitutional law. The Supreme Court applied the equal protection clause on May 17, 1954, when it ruled that states that segregated white and black children in the public schools violated the Constitution (Brown v. Board of Education of Topeka).

Under Article V, amendments to the Constitution 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. All subsequent amendments have been initiated by Congress. Amendments that have been proposed by Congress must be ratified by three-fourths of the state legislatures or by conventions in as many states. Congress decides which method will be used and sets the time limit for ratification.

Twenty-seven amendments have been added to the Constitution since 1789. In addition to the first 10--the Bill of Rights of 1791 was adopted as a single unit--far-reaching amendments include the Thirteenth (1865), abolishing slavery, the Fourteenth (1868), discussed previously, and the Fifteenth (1870), guaranteeing the right to vote regardless of race. The Seventeenth (1913) provides for direct election of U.S. Senators and the Nineteenth (1920) for woman suffrage. The Twenty-second (1951) limits the presidency to two terms. The Twenty-sixth (1971) granted suffrage to citizens 18 and older.