According to Article V of the Constitution, an amendment must either be proposed by Congress with a two-thirds majority vote in both the House of Representatives and the Senate, or by a constitutional convention called for by two-thirds of state legislatures. Either way, a proposed amendment only becomes part of the Constitution when ratified by legislatures or conventions in three-fourths of the states (38 of 50 states).

Since the Constitution was ratified in 1789, hundreds of thousands of bills have been introduced attempting to amend it. But only 27 amendments to the U.S. Constitution have been ratified, out of 33 passed by Congress and sent to the states. Under Article V, states also have the option of petitioning Congress to call a constitutional convention if two-thirds of state legislatures agree to do so. This has never occurred, though state legislatures have passed hundreds of resolutions over the years calling for a constitutional convention over issues ranging from a balanced budget to campaign finance reform.

Here is a summary of the 27 amendments to the Constitution:

In order to secure support for the Constitution among Anti-Federalists, who feared it gave too much power to the national government at the expense of individual states, James Madison agreed to draft a Bill of Rights during the first session of Congress. Of these first 10 amendments, the First Amendment is arguably the most famous and most important. It states that Congress can pass no law that encroaches on an American freedom of religion, freedom of speech, freedom of the press, freedom to assemble and freedom to petition the government. These fundamental rights of thought and expression go to the heart of the revolutionary idea of popular government, as envisioned in the Declaration of Independence.

The text of the Second Amendment reads: “A well-regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed.” During the Revolutionary War era, “militia” referred to groups of men who banded together to protect their communities, towns, colonies and eventually states.

Differing interpretations of the amendment have fueled a long-running debate over the original intention of the Second Amendment. The crux of the debate is whether the amendment protects the right of private individuals to keep and bear arms, or whether it instead protects a collective right that should be exercised only through formal militia units. Those who argue it is a collective right point to the “well-regulated Militia” clause in the Second Amendment. Gun rights supporters, as well as Supreme Court decisions such as District of Columbia v. Heller (2008), have argued the Second Amendment protects the right of an individual person to keep and bear arms for the purposes of self defense.

This amendment prohibits the quartering of militia in private homes in either war or peacetime without consent of the homes’ owners. As a reaction against past laws allowing British soldiers to take shelter in colonists’ homes whenever they wanted, the Third Amendment doesn’t appear to have much constitutional relevance today, as the federal government is unlikely to ask private citizens to house soldiers. The Supreme Court has never decided a case on the basis of the Third Amendment, but it has referred to its protections in cases surrounding issues of property and privacy rights.

The Fourth Amendment’s guarantee of “the right of the people to be secure in their persons, houses, papers and effects, against unreasonable searches and seizures” also grew directly out of colonial Americans’ experiences prior to the Revolutionary War. Most notably, British authorities made use of general warrants, which were court orders that allowed government officials to conduct searches basically without limitations. Beginning in the 20th century, with the growth in power of federal, state and local law enforcement, the Fourth Amendment became an increasingly common presence in legal cases, limiting the power of the police to seize and search people, their homes and their property and ensuring that evidence gathered improperly could be excluded from trials.

In addition to the famous right to refuse to testify against oneself (or “plead the Fifth”), the Fifth Amendment establishes other key rights for defendants in criminal proceedings, including the need for formal accusation by a grand jury and the protection against double jeopardy, or being tried for the same crime twice. It also requires the federal government to pay just compensation for any private property it takes for public use. Most importantly, the Fifth Amendment guarantees that no one can face criminal punishment without receiving “due process of law,” a protection that the Supreme Court later extended under the due process clause of the 14th Amendment.

The Sixth Amendment also deals with protecting the rights of people against possible violations by the criminal justice system. It ensures the right to a public trial by an impartial jury without a significant delay and gives defendants the right to hear the charges against them, call and cross-examine witnesses and retain a lawyer to defend them in court.

According to the modern interpretation of the amendment—shaped by Supreme Court cases such as Powell v. Alabama (1932), which involved the defendants known as the Scottsboro Boys—the state is required to provide effective legal representation for any defendant who cannot afford to employ a lawyer on their own.

With the Seventh Amendment, Madison addressed two Anti-Federalist concerns: that the document failed to require jury trials for civil (non-criminal) cases, and that it gave the Supreme Court the power to overturn the factual findings of juries in lower courts. Considered one of the most straightforward amendments in the Bill or Rights, the Seventh Amendment extends the right to a jury trial to federal civil cases such as automobile accidents, property disputes, breach of contract, and discrimination lawsuits. It also prevents federal judges from overturning jury verdicts based on questions of fact, rather than law. Unlike nearly every other right in the Bill of Rights, the Supreme Court has not extended the right to civil jury trial to the states, although most states do guarantee this right.

The Eighth Amendment continues the theme of the Fifth and Sixth Amendments by targeting potential abuses on the part of the criminal justice system. In banning the requirement of “excessive bail,” the imposition of “excessive fines,” and the infliction of “cruel and unusual punishment,” but leaving the exact interpretation of these terms unclear, it paved the way for future generations to battle over their meaning. In particular, differing opinions over what constitutes “cruel and unusual punishment” fuel the ongoing debate in the United States over capital punishment.

During the debate that produced the Bill of Rights, skeptics argued that by listing such fundamental rights in the Constitution, the framers would be implying that the rights they did not list did not exist. Madison sought to allay these fears with the Ninth Amendment. It ensures that even while certain rights are enumerated in the Constitution, people still retain other non-enumerated rights.

Legal scholars and courts have long debated the meaning of the Ninth Amendment, particularly whether or not it provides a foundation for such rights as privacy (as in the 1965 case Griswold v. Connecticut) or a woman’s right to an abortion (1973’s Roe v. Wade).

As the final amendment in the Bill of Rights, the 10th Amendment originally aimed to reassure Anti-Federalists by further defining the balance of power between the national government and those of the individual states. According to the 10th Amendment, the federal government’s powers are limited to those expressly given to it by the Constitution, while all other powers are reserved for the states or the people. Over the generations, debate has continued over which powers fall into this latter category, and what limitations should be placed on the expanding powers of the federal government.

The first amendment to be ratified after the Bill of Rights, the 11th Amendment was also the first to be framed in direct response to a Supreme Court verdict. In Chisholm v. Georgia (1793), the Court had ruled that the plaintiff, a resident of South Carolina, had the right to sue Georgia for repayment of debts incurred during the Revolutionary War. After many states argued that using the federal courts in this way would shift too much power to the national government, Congress passed the 11th Amendment, which removes all cases involving suits between states from federal court jurisdiction.

Passed in the wake of the chaotic presidential election of 1800, in which Thomas Jefferson and his fellow Democratic-Republican Aaron Burr received the exact same number of votes in the Electoral College, the 12th Amendment provides the method for selecting president and vice president of the United States. Though Article II, Section 1 of the Constitution had mandated that each elector cast two votes without differentiating between their choices for president and vice president, the 12th Amendment requires electors to split the balloting for the two offices.

More than six decades passed between ratification of the 12th and 13th Amendments. With the United States roiled by sectional tensions over slavery, few in the post-founding generations wanted to provoke a constitutional crisis by proposing a potentially divisive amendment. But after Abraham Lincoln issued the Emancipation Proclamation, which freed only enslaved people behind enemy lines during the Civil War, support grew for a constitutional amendment to abolish slavery. Ratified after Lincoln’s assassination, the 13th Amendment finally put an end to the institution that had marred the country since 1619.

Intended to give Congress the authority to protect the rights of Black citizens in the South, where white-dominated state governments enacted discriminatory “Black codes” immediately following the end of the Civil War, the 14th Amendment was arguably the most important of the three amendments passed during Reconstruction. Section 1 of the amendment reversed the Supreme Court’s notorious decision in 1857’s Dred Scott v. Sandford by stating that anyone born in the United States is a citizen. It also extended the civil rights of citizens and their right to due process by protecting civil rights from infringement by the states as well as the federal government. Finally, Section 1 guarantees “equal protection under the laws” to all citizens.

Together with the Bill of Rights, these broad protections form the foundations of civil rights law in the United States, and have been invoked over the years by various groups of citizens (as well as corporations) seeking equal treatment under the law.

Section 2 of the 14th Amendment repealed the three-fifths clause of the original Constitution, which held that each enslaved person counted for three-fifths of a person. It specified that every resident of a state should be counted as a full person for the purposes of congressional representation. Section 3, aimed at former Confederate leaders, holds that Congress can bar any official who “shall have engaged in insurrection or rebellion” against the United States from holding public office. Section 4 exempted federal and state governments from paying any debts incurred by the former Confederate states or compensating them for the loss of their human property. Finally, Section 5 of the 14th Amendment gives Congress the authority to create laws to enforce the amendment’s provisions, a sweeping mandate that would strengthen the power of the federal government in relation to the states.

After Congress enfranchised Black male voters in the South by passing the Reconstruction Act of 1867, it sought to protect this right under the Constitution. As the last of the so-called Civil War amendments, all of which sought to ensure equality for African Americans, the 15th Amendment outlaws discrimination in voting rights on the basis of race, color or previous condition of servitude. With the end of Reconstruction in 1877, however, Southern states effectively disenfranchised Black voters by enacting poll taxes, literacy tests and other discriminatory practices. The promise of the 15th Amendment to protect Black voting rights remained unfulfilled until the civil rights movement and passage of the Voting Rights Act of 1965.

Though Americans had paid income taxes in earlier eras (during the Civil War, for example), the Supreme Court ruled in 1894’s Pollock v. Farmer’s Loan and Trust that an income tax imposed by Congress was unconstitutional given Article I’s requirement that such “direct” taxes be apportioned among the states on the basis of population. The decision drew widespread outrage, and led to the passage of the first of four constitutional amendments that would be ratified during the Progressive era. The 16th Amendment gives Congress the power to enact a nationwide income tax, vastly expanding the federal government’s source of revenue and spending power and enabling it to become a stronger force in American life than ever before.

The movement in favor of the popular election of senators gained strength in the late 19th century, fueled by a view of the Senate as an out-of-touch, elitist group subject to corruption. By 1912, many state legislatures had lent their vocal support to the change, leading to ratification of the 17th Amendment the following year. The amendment substantially altered the structure of Congress as set out in Article I of the Constitution, removing from state legislatures the power to choose U.S. senators and giving it directly to the voters of each state.

Though the temperance movement had existed since the earliest years of the nation’s history, it gained strength during the Progressive Era, especially in rural American communities. The new income tax freed the government from its dependence on the liquor tax, and senators (now directly elected) were subject to greater pressure from temperance advocates. Congress followed up on ratification of the 18th Amendment, which banned “the manufacture, sale, or transportation of intoxicating liquors,” but not their consumption, with passage of the Volstead Act to enforce it. Prohibition remained in effect for the next 13 years, until its repeal with the 21st Amendment.

Susan B. Anthony and other supporters of women’s suffrage were bitterly disappointed after the Civil War, when Congress excluded gender from the list of categories that could not be used to deny voting rights in the 15th Amendment. With a constitutional amendment stalled in Congress for decades, suffragists focused their efforts on the states, where they were able to make gradual progress. By the time the 19th Amendment was ratified in 1920, forbidding the United States or any state from denying or abridging the right to vote to any citizen “on account of sex,” 30 states and one territory allowed women to vote in at least some elections. Even after ratification of the 19th Amendment, many women of color were subject to various types of voter suppression until passage of the Voting Rights Act of 1965.

Before ratification of the 20th Amendment, 13 months had passed between the election of a new Congress and the time it held its first meeting. The amendment shortened this “lame-duck” period by specifying that regular terms for members of the Senate and House of Representatives begin on January 3 of the year following their election. It also moved up the inauguration of the president by six weeks, moving it to January 20. The 20th Amendment was quickly proposed, passed and ratified during the Great Depression, when many people regretted that Franklin D. Roosevelt had to wait four months to succeed the unpopular Herbert Hoover.

Prohibition became widely unpopular during the Depression, especially in American cities, where some demonstrators marched in parades carrying signs declaring “We Want Beer.” The 21st Amendment, which ended Prohibition and left the states in charge of regulating the sale and consumption of liquor, is the only amendment that repeals an earlier amendment (the 18th). It’s also the only one to be ratified by state ratifying conventions rather than state legislatures. As the temperance movement still held sway in many states, supporters of the 21st Amendment realized that state legislators could be subject to political pressure, and opted to follow the convention route instead.

Though term limits were not a part of the Constitution, later generations of Americans believed that George Washington set a valuable precedent when he made the decision to step away from the presidency after two terms in 1796. Several later presidents flirted with the idea of a third term, but Franklin D. Roosevelt was the first to follow through. Guiding the nation through the tumultuous era spanning the Depression and World War II, FDR won an unprecedented four presidential elections, but died several months after his fourth term began in 1945. Two years later, Congress began the process of passing the 22nd Amendment, which limited future presidents to two terms.

Since the District of Columbia became the seat of the U.S. government in 1800, debate had raged over the inability of its residents to participate in federal elections. The 23rd Amendment addressed this, giving D.C. residents the right to choose electors for presidential and vice-presidential elections in the same way the states do. While the original version of the amendment approved by the Senate would have granted the District representation in the House of Representatives, the House rejected this idea. In 1978, Congress adopted another proposed amendment that provided for D.C. to “be treated as though it were a State,” including congressional representation, but it failed to win ratification.

Starting in the years following Reconstruction, many white-dominated Southern legislatures enacted poll taxes as a method of disenfranchising Black voters. Congress repeatedly debated legislation to eliminate poll taxes starting in 1939, but none passed. Though only five states still had such taxes in place by 1964, supporters of the civil rights movement saw their abolition as an important objective in combating racism and discrimination against Black Americans. The 24th Amendment applied only to federal elections, and after its ratification several southern states tried to maintain poll taxes for separately held state elections. In Harper v. Virginia Board of Elections (1966), the Supreme Court deemed such taxes a violation of the 14th Amendment’s equal protection clause.

After John F. Kennedy was assassinated in November 1963, a movement grew to clarify the vague procedures that had existed around presidential disability and the right of succession. The 25th Amendment states that the vice president will succeed the president in case of the latter’s death or resignation, and lays out the procedure for filling a vacancy in the vice president’s office. It also allows the president to declare a temporary inability to serve—as in the case of undergoing surgery—and resume powers when able. The fourth and most controversial section, which has never been invoked, empowers the vice president to become acting president if the president is determined (by the vice president and the majority of the Cabinet, backed by Congress) to be unable to perform the duties of the office.

The long-running debate over whether young Americans should be asked to risk their lives fighting for their country before they were given the right to vote intensified during the Vietnam War. In 1970, Congress passed a statute lowering the age of voting in all federal, state and local elections to 18. When Oregon challenged that law, the Supreme Court sided with the state, ruling that Congress only had jurisdiction over federal elections. With a groundswell of popular support, the 26th Amendment was passed and ratified in record time, lowering the legal voting age to 18 in all U.S. elections.

By prohibiting any law raising or lowering the salaries of members of Congress from taking effect before the start of a new session of Congress begins, the 27th Amendment aims to reduce corruption in the legislative branch of the federal government. Originally introduced by Madison, it was left in limbo when the first 10 amendments were ratified in 1791 and largely forgotten by the late 20th century, when Gregory Watson, a college student in Texas, read about it in a class on American government. Watson later rallied enough popular support (and resentment of Congress) to get the requisite three-quarters of U.S. states to ratify the 27 Amendment by 1992, nearly 200 years after Madison first proposed it.

Constitutional Amendment Process. Federal Register, National Archives.

Jack N. Rakove, ed. The Annotated U.S. Constitution and Declaration of Independence. (Harvard University Press, 2009)

The Heritage Guide to the Constitution. Heritage Foundation.

Interactive Constitution. Constitution Center.