Congress has two chambers: the House of Representatives and the Senate. Together they form the bicameral legislature that Article I of the Constitution vests with all federal lawmaking power, and no bill becomes law unless both chambers pass it in identical form.1Congress.gov. Constitution of the United States – Article I The framers built the two-chamber structure at the 1787 Constitutional Convention as a check against concentrating too much power in a single legislative body.
The two chambers look parallel on paper but work very differently. The House is large, fast-moving, and pegged tightly to population. The Senate is small, slow, and gives every state the same voice. What follows is what each one is, what each one does that the other cannot, and how they combine to produce a law.
The House of Representatives
The House is the larger chamber, with 435 voting members. Seats are divided among the states by population, and the 435 total has been fixed since the Permanent Apportionment Act of 1929, now codified at 2 U.S.C. ยง2a.2Congressional Research Service. Size of the U.S. House of Representatives The total does not change, but after each ten-year census the seats are redistributed to match population shifts. A state that gained residents may pick up a seat; a state that lost residents may lose one.
To serve in the House, a person must be at least 25 years old, have been a U.S. citizen for at least seven years, and live in the state where they are elected.3Constitution Annotated. Article I Section 2 – House of Representatives Terms run two years, and every seat is on the ballot in every even-numbered year. That short cycle keeps House members closely tied to voter sentiment.
The Constitution gives the House two powers the Senate does not share. Every bill that raises revenue must originate in the House.4Congress.gov. U.S. Constitution Article I Section 7 And the House holds the sole power of impeachment, meaning it is the only body that can formally charge a federal official with misconduct.5Congress.gov. ArtI.S2.C5.1 Overview of Impeachment Impeachment works like an indictment: the House brings the charges, and the Senate holds the trial.
The House is led by the Speaker, elected by the full membership, though in practice the job goes to a member of the majority party. The Speaker controls the flow of legislation, presides over debates, and sits second in the presidential line of succession behind the Vice President.6U.S. Senate. Presidential Succession Act
The United States Senate
The Senate is the smaller chamber, with exactly 100 members. Every state gets two senators regardless of population, so Wyoming’s roughly 580,000 residents have the same Senate representation as California’s nearly 39 million.7Congress.gov. Constitution Annotated – Article I Section 3 Equal state representation was the compromise that persuaded smaller states to join the union.
Senators must be at least 30 years old, have been U.S. citizens for at least nine years, and live in the state they represent.8Congress.gov. Article 1 Section 3 Clause 3 – Qualifications Terms run six years, staggered so that roughly one-third of the seats are up every two years.9U.S. Senate. Qualifications and Terms of Service The chamber never turns over all at once, which gives it more institutional continuity than the House. Senators were originally chosen by state legislatures; the 17th Amendment, ratified in 1913, shifted the process to direct popular election.10Constitution Annotated. Seventeenth Amendment
The Senate’s signature constitutional role is “advice and consent.” The president cannot finalize appointments to the Supreme Court, the cabinet, or ambassadorships without Senate approval, and the same provision requires a two-thirds Senate vote to approve international treaties.11Congress.gov. Constitution Annotated – Article II Section 2 Clause 2 Strictly speaking, the Senate does not ratify a treaty itself; it approves a resolution of ratification, which the president then completes.12United States Senate. About Treaties The Senate also has exclusive authority to try impeachments; senators sit as the jury, and conviction and removal require a two-thirds vote.13U.S. Senate. About Impeachment
The Senate’s presiding officer is technically the Vice President of the United States, who votes only to break a tie.14Congress.gov. Article 1 Section 3 Clause 4 Because the Vice President rarely appears for routine business, the Senate elects a President Pro Tempore, traditionally the longest-serving member of the majority party, who is next in the line of presidential succession after the Speaker.6U.S. Senate. Presidential Succession Act
How the Two Chambers Differ in Practice
The clearest working difference between the chambers is how each handles debate. In the House, the Rules Committee sets strict time limits and decides which amendments can be offered on any given bill; sometimes it allows broad debate with many amendments, sometimes none at all.15Congress.gov. The Legislative Process: House Floor With 435 members, that kind of structure is the only way to move business through the chamber.
The Senate runs with far fewer constraints. Any senator can hold the floor and extend debate on a bill indefinitely, a tactic known as a filibuster. Cutting off debate requires cloture, and under Senate Rule XXII cloture takes 60 of 100 senators.16U.S. Senate. About Filibusters and Cloture If the 60 votes are not there, a bill can stall even when a simple majority supports it. The 60-vote threshold does not apply to nominations, where rule changes in the 2010s allow a simple majority to end debate. The practical result: passing a bill through the Senate is harder than passing the same bill through the House.
Party leadership drives the day-to-day work in both chambers. Majority and minority leaders, chosen by their party caucuses, set strategy, and party whips coordinate votes and keep members aligned on key legislation.
How Both Chambers Pass a Law Together
A bill cannot reach the president’s desk until the House and Senate pass it in identical form. In practice the two chambers almost always produce different versions of the same legislation. One chamber adds an amendment, changes a funding level, or rewrites a provision, and the two bills no longer match.
When that happens, Congress has options. Sometimes one chamber simply votes to accept the other’s version. More often, leadership forms a conference committee of members from both chambers to negotiate a compromise. Once the conference committee agrees on unified language, the House and Senate each vote on that final version, and no further amendments are allowed at that stage. Only after both chambers approve the identical text does the bill go to the president for signature or veto.
Filling a Vacant Seat
The chambers handle mid-term vacancies differently. When a House seat opens because a member dies, resigns, or is removed, it can be filled only through a special election called by the state’s governor; a governor cannot appoint a replacement to the House. The specific timing depends on state law and how far into the two-year session the vacancy occurs.17Office of the Historian, U.S. House of Representatives. Vacancies and Successors
When a Senate seat opens, the 17th Amendment directs the governor to call a special election, and most states also authorize their governors to appoint an interim senator to serve until that election. Only a handful of states require the seat to stay vacant until voters fill it.18Congressional Research Service. U.S. Senate Vacancies: How Are They Filled?