Article I of the United States Constitution creates Congress and defines the federal government’s lawmaking power. It is the longest article in the Constitution, and it does three big things: it builds the legislature out of two chambers, it lists the specific powers Congress holds, and it draws lines around what Congress and the states are not allowed to do.
Two Chambers, One Congress
All federal legislative power belongs to Congress, which is split into the House of Representatives and the Senate.1Constitution Annotated. Article I – Legislative Branch The two-chamber design came out of a compromise at the Constitutional Convention. Population-heavy states wanted representation tied to their size; smaller states wanted equal footing. The House answers the first demand, the Senate the second.
House seats are distributed among the states by population, with a total of 435 seats reallocated after each decennial census.2United States Census Bureau. Congressional Apportionment Every state gets exactly two senators no matter its size.
Who Serves and For How Long
House members serve two-year terms. A candidate must be at least twenty-five years old, a U.S. citizen for at least seven years, and a resident of the state they represent. When a House seat opens mid-term, the governor of that state must call a special election.3Constitution Annotated. Article I Section 2
Senators serve six-year terms and must be at least thirty, a citizen for nine years, and a resident of their state.4National Archives. The Constitution of the United States – A Transcription Terms are staggered so that about a third of the Senate is up for election every two years, which keeps the chamber from ever turning over all at once. Originally, state legislatures chose senators; the Seventeenth Amendment, ratified in 1913, changed that to direct election by the voters. It also governs mid-term vacancies: the governor calls a special election, and the state legislature can authorize a temporary gubernatorial appointment in the meantime.5Congress.gov. U.S. Constitution – Seventeenth Amendment
The House picks its own Speaker, who controls the floor schedule. The Vice President of the United States is the Senate’s presiding officer but votes only to break a tie. When the Vice President is absent, a President pro tempore chosen by the Senate takes the chair.4National Archives. The Constitution of the United States – A Transcription
How a Bill Becomes Law
A bill can be introduced in either chamber, with one exception: revenue-raising bills must originate in the House.6Constitution Annotated. ArtI.S7.C1.1 Origination Clause and Revenue Bills The framers put revenue power in the chamber closest to the voters. Both chambers must pass identical text before the bill goes any further, and a simple majority of the total membership must be present in each chamber to conduct business at all.7Congress.gov. Article I Section 5
Once both chambers agree, the bill goes to the President, who has ten days (Sundays excluded) to act. Signing makes it law. Doing nothing while Congress is still in session also makes it law when those ten days expire. If the President objects, the bill returns to Congress with a written explanation.8Constitution Annotated. Article I Section 7
Congress can override a veto, but the threshold is steep: two-thirds of both chambers. There is also the pocket veto. If Congress adjourns during the ten-day window, the President can kill the bill just by not signing it. With Congress adjourned, the bill cannot become law automatically and there is no chance to attempt an override.8Constitution Annotated. Article I Section 7
What Congress Can Do
Section 8 is the heart of Article I. It lists the specific powers Congress holds, and a great deal of what the federal government does today traces back to one of these clauses.9Constitution Annotated. Article I Section 8
Money, Taxes, and Debt
Congress can levy taxes to pay debts and fund national defense and the general welfare, with rates required to be uniform across the states. It can borrow money on the nation’s credit. That borrowing power runs today through a statutory debt limit codified at 31 U.S.C. § 3101, which caps outstanding federal obligations.10Office of the Law Revision Counsel. 31 USC 3101 – Public Debt Limit Congress also coins money, sets its value, and fixes standards of weights and measures.
Commerce and Bankruptcy
The Commerce Clause lets Congress regulate trade with foreign nations, between states, and with Indian tribes. This is the constitutional basis for a huge portion of federal regulation, because almost any economic activity has some connection to interstate commerce. Congress also writes uniform bankruptcy laws so the rules for financial failure do not vary by state line.
Patents and Copyrights
Congress can grant authors and inventors exclusive rights to their works and discoveries for limited periods.11Congress.gov. Overview of Congress’s Power Over Intellectual Property This is the foundation of the federal patent and copyright system, which Congress has operated continuously since 1790.
War and the Military
Only Congress can declare war. It raises and funds the armed forces, but military appropriations cannot run for more than two years at a time, a check against permanent standing armies. Congress provides for a navy (with no similar time limit), writes rules for military conduct, and controls the militia, though states retain the power to appoint militia officers and train their own forces.
Everything Else, and the Elastic Clause
Section 8 also authorizes Congress to establish post offices, create federal courts below the Supreme Court, punish piracy, and govern the federal district that became Washington, D.C. The final clause is the most open-ended: Congress can make any law that is necessary and proper to carry out the powers listed above. Sometimes called the Elastic Clause, it lets the federal government respond to problems the framers never imagined.
What Congress Cannot Do
Section 9 restricts Congress itself. The framers understood that a powerful legislature could threaten liberty as easily as a king could.
- Habeas corpus cannot be suspended except during rebellion or invasion when public safety demands it. The government cannot hold someone in custody indefinitely without bringing them before a court.12Constitution Annotated. Article I Section 9 – Powers Denied Congress
- Bills of attainder are prohibited. Congress cannot pass a law declaring a specific person guilty of a crime; that job belongs to the courts.
- Ex post facto laws are prohibited. Conduct that was legal when you did it cannot be criminalized retroactively.
- Titles of nobility cannot be granted, and federal officeholders cannot accept gifts, titles, or payments from foreign governments without congressional approval.13Congress.gov. Article I Section 9 Clause 8
- Spending requires an appropriation authorized by law, and Congress must publish a regular accounting of receipts and expenditures.
Section 9 originally required direct taxes to be apportioned among the states by population, which made a broad income tax impractical. The Sixteenth Amendment, ratified in 1913, removed that obstacle and authorized Congress to tax income from any source without apportionment.14Legal Information Institute. Direct Taxes and the Sixteenth Amendment That amendment is why the federal income tax exists in its modern form.
What States Cannot Do
Section 10 turns the restrictions outward. States cannot enter treaties or alliances with foreign governments, coin their own money, or issue their own paper currency.15Constitution Annotated. Article I Section 10 – Powers Denied States They cannot pass laws that impair the obligation of contracts. Like Congress, they cannot pass bills of attainder, enact ex post facto laws, or grant titles of nobility.
States also cannot impose tariffs on imports or exports without congressional consent, aside from fees strictly needed to enforce inspection laws. They cannot keep standing armies or warships in peacetime, and they cannot engage in war unless actually invaded or facing danger too immediate to wait. These limits keep foreign policy, national defense, and interstate commerce under federal control.
Impeachment
Article I splits impeachment between the two chambers. The House alone can impeach, meaning it investigates and votes on formal charges called articles of impeachment. A simple majority is enough.16USAGov. How Federal Impeachment Works Impeachment is not removal; it is closer to an indictment.
The Senate then holds the trial. If the person on trial is a sitting President, the Chief Justice of the United States presides. Conviction requires a two-thirds vote of the senators present, and the consequences are removal from office and possible disqualification from holding future federal office.17U.S. Senate. About Impeachment Any criminal prosecution is a separate matter in the courts.
Amendments That Changed Article I
Several later amendments rewrote parts of Article I as originally drafted:
- The Twelfth Amendment aside, the Fourteenth Amendment’s Section 2 replaced the three-fifths clause and required representatives to be apportioned based on the whole number of persons in each state.18Constitution Annotated. Fourteenth Amendment Section 2
- The Sixteenth Amendment authorized a federal income tax without apportionment.
- The Seventeenth Amendment shifted senator selection from state legislatures to direct popular election.
- The Twenty-Seventh Amendment delays any congressional pay change until after the next House election, giving voters a say before a raise takes effect.19Congress.gov. Article I Section 6 Clause 1
Read together, Article I and the amendments that revised it describe the machinery of American lawmaking: who gets to write federal law, how they are chosen, what they can pass, what they cannot touch, and how a bill becomes binding on the country.