Article I of the Constitution creates the United States Congress and defines the scope of federal legislative power. It is the longest article in the document, running ten sections that cover who can serve in Congress, how laws get made, what the federal government is allowed to do, and what both Congress and the states are forbidden from doing. The framers put the legislature first on purpose: lawmaking belongs to elected representatives before any other branch enters the picture.
The Two Chambers of Congress
Congress is split into a House of Representatives and a Senate. Every proposed law has to clear both before it can reach the President, and the two bodies are built with different incentives so they check each other.
The House
A House member must be at least 25 years old, a U.S. citizen for at least seven years, and an inhabitant of the state where they are elected. The Constitution uses the word “state,” not “district,” so the residency rule is broader than many people assume.1Library of Congress. ArtI.S2.C2.1 Overview of House Qualifications Clause Representatives serve two-year terms, which keeps them close to shifts in public opinion.
Seats are apportioned by population and recalculated after each ten-year census. The Constitution itself sets no total; Congress capped the House at 435 members through the Permanent Apportionment Act of 1929.2US House of Representatives. The 1911 House Reapportionment The original text also included the Three-Fifths Compromise for counting enslaved people. The Fourteenth Amendment eliminated that formula after the Civil War and required counting “the whole number of persons in each State.”3Constitution Annotated | Congress.gov. Article I Section 2 Clause 3
The House chooses its own Speaker and holds the sole power of impeachment, meaning only the House can formally charge a federal official with misconduct.4Congress.gov. Overview of Impeachment
The Senate
Senators face stiffer requirements: at least 30 years old, nine years of citizenship, and residency in the state they represent.1Library of Congress. ArtI.S2.C2.1 Overview of House Qualifications Clause Every state gets two senators regardless of population, which gives smaller states equal footing with larger ones. Terms run six years, staggered so roughly a third of the seats turn over every two years. That structure insulates the Senate from sudden shifts in public mood.
Originally, state legislatures chose senators. The Seventeenth Amendment, ratified in 1913, gave that choice directly to voters.5National Archives. 17th Amendment to the U.S. Constitution – Direct Election of U.S. Senators The Vice President presides over the Senate but only votes to break a tie.6United States Senate. Votes to Break Ties in the Senate
How a Bill Becomes Law
Section 7 lays out the path. Any bill that raises revenue has to start in the House, keeping tax power closest to the members who face voters every two years. The Senate can amend those bills freely but cannot originate them.7Constitution Annotated. U.S. Constitution Article I Section 7
Both chambers must pass identical text before a bill reaches the President. A signature makes it law. A veto sends it back to the chamber where it started, and Congress can override that veto only with a two-thirds vote in both the House and Senate.8Congress.gov. ArtI.S7.C2.1 Overview of Presidential Approval or Veto of Bills
If the President does nothing for ten days (Sundays excluded) while Congress is in session, the bill becomes law without a signature. If Congress adjourns before those ten days run out, the President can kill the bill just by holding it. That is a pocket veto, and Congress has no override. The only path forward is to reintroduce the bill in a later session.9Legal Information Institute. The Veto Power
What Congress Can Do
Section 8 spells out federal legislative power in eighteen numbered clauses.10Constitution Annotated. U.S. Constitution Article I Section 8 The consequential ones fall into a few groups.
Taxing, Spending, and Borrowing
Congress can levy taxes, duties, and excises to pay debts and fund the common defense and general welfare. It can borrow money on the nation’s credit, which is the constitutional basis for the national debt. The spending power also carries leverage over states: under South Dakota v. Dole (1987), Congress can attach conditions to federal funds it sends to states as long as those conditions are clear, related to the program, and not so financially coercive that states have no real choice but to comply.
Commerce
The Commerce Clause lets Congress regulate trade with foreign nations and among the states. This one clause has become the constitutional foundation for an enormous range of federal law, from workplace rules to environmental regulation. The Supreme Court has read it broadly, allowing Congress to reach intrastate activity that has a substantial effect on interstate commerce. The Court has occasionally pushed back: in United States v. Lopez (1995), it struck down a federal gun-free school zone law because the link to interstate commerce was too thin.
Money, Mail, and Ideas
Congress coins money and sets its value, writes uniform bankruptcy and naturalization laws for all states, runs the post office, and grants patents and copyrights for limited periods.10Constitution Annotated. U.S. Constitution Article I Section 8
War and Armed Forces
Only Congress can declare war. It raises and funds the army, maintains the navy, and calls up state militias to enforce federal law, put down insurrections, or repel invasions. The framers added one built-in restraint: army funding cannot be appropriated for longer than two years at a time, forcing regular legislative review of military spending. Congress also creates federal courts below the Supreme Court and defines punishments for crimes on the high seas.
The Necessary and Proper Clause
Clause 18 lets Congress make all laws “necessary and proper” for carrying out its other listed powers.11Constitution Annotated. Article I Section 8 Clause 18 Often called the Elastic Clause, it is what allows the federal government to adapt to problems the framers never anticipated. The Supreme Court cemented its reach in McCulloch v. Maryland (1819), ruling that Congress could charter a national bank even though banking is nowhere in the text. Chief Justice Marshall wrote that if the end is legitimate and within the Constitution, and the means are appropriate and not prohibited, those means are constitutional.12National Archives. McCulloch v. Maryland (1819) Federal agencies, paper currency, and the interstate highway system all rest on this clause.
What Congress Cannot Do
Section 9 lists limits on federal power. The most fundamental is the writ of habeas corpus, the right to challenge your detention before a judge. Congress can only suspend that right during rebellion or invasion when public safety demands it. Congress also cannot pass bills of attainder, which single out a person or group for punishment without a trial, and it cannot pass ex post facto laws that criminalize conduct after the fact.13Constitution Annotated. Constitution Annotated – Article I Section 9
On money: Congress cannot tax goods exported from any state.14Constitution Annotated | Congress.gov. Article I Section 9 Clause 5 Direct taxes must be apportioned among the states by population. No money can leave the treasury without a specific appropriation authorized by law, and the government must publish a regular accounting of receipts and expenditures. The Sixteenth Amendment, ratified in 1913, carved out the big exception to apportionment by allowing Congress to levy an income tax without dividing the total among states by population. That is how the modern federal income tax works.
Section 9 also bars the federal government from granting titles of nobility. Federal officeholders cannot accept gifts, payments, or titles from foreign governments without congressional consent.15Constitution Annotated. Article I Section 9 Clause 8 This foreign emoluments provision has drawn renewed attention in recent years as courts have considered its scope against modern business interests.
What States Cannot Do
Section 10 restricts state governments to keep them from running their own foreign policy or undermining the national economy. States cannot enter treaties or alliances with foreign powers or with each other. They cannot coin money, issue paper currency, or make anything other than gold and silver legal tender for debts.16Constitution Annotated. Article I Section 10 – Powers Denied States
The same prohibitions on bills of attainder and ex post facto laws that bind Congress also bind every state. States cannot grant titles of nobility, and they cannot tax imports or exports without congressional approval beyond what is absolutely necessary to enforce their inspection laws. States also cannot keep troops or warships in peacetime or wage war unless actually invaded or facing an imminent threat that cannot wait for federal action.16Constitution Annotated. Article I Section 10 – Powers Denied States
Impeachment
Article I splits impeachment between the two chambers. The House acts like a grand jury, investigating and voting on whether to bring charges. A simple House majority is enough to impeach.4Congress.gov. Overview of Impeachment The Senate then holds the trial. When the President is on trial, the Chief Justice presides. Conviction requires a two-thirds vote of the senators present.17U.S. Senate. About Impeachment The maximum penalty is removal from office. The Senate can also vote separately, by simple majority, to bar the convicted official from ever holding federal office again.18Legal Information Institute. Overview of Impeachment Judgments Impeachment is a political process, not a criminal one. A convicted official can still face separate criminal prosecution in the regular courts.