The House of Representatives is the larger of the two chambers of the Congress of the United States. Members of the House of Representatives (usually called congressmen, congresswomen, or representatives) serve 2-year terms; the entire membership stands for reelection every second year. To serve in the House of Representatives, a person must be at least 25 years old, a U.S. citizen for at least 7 years, and, at the time of election, a resident of the state in which he or she is chosen.

Seats in the House of Representatives are apportioned among the states on the basis of population. Reapportionments and redistricting occur, where necessary, after each decennial census. Some states gain and other states lose seats in these reapportionments, but the Constitution of the United States requires that all states retain at least one representative regardless of population. When the House met for the first time on Mar. 4, 1789, in New York City, it had 59 members; each represented a district of approximately 30,000 people. The size of the House grew steadily until 1912, when, by act of Congress, membership was stabilized at the current figure of 435. As a result of the 2010 census, the average size of a congressional district grew to 710,767 people. In addition to the representatives, there is a nonvoting resident commissioner from Puerto Rico, who is elected for a 4-year term. Nonvoting delegates, elected to 2-year terms, represent American Samoa, the Commonwealth of Northern Mariana Islands, the District of Columbia, Guam, and the Virgin Islands. The resident commissioner and the delegates may participate in debate and vote in committees. House seats vacated by death or other reason can only be filled by special elections. (Senate vacancies are temporarily filled by state governors until special elections can be held.)

Since the mid-19th century most representatives have been members of the Democratic or Republican parties. The larger of the two groups at any given time is called the majority party and has primary responsibility for organizing the House.

The presiding officer of the House is the Speaker, who is traditionally the leader of the majority party. The Speaker is elected at the beginning of each 2-year term of Congress by the full membership of the House. Some Speakers have been vested with great formal powers that enabled them to dominate the House. Among the most powerful Speakers were Thomas Brackett Reed of Maine (1889–91, 1895–99) and Joseph G. Cannon of Illinois (1903–11). After Cannon, the formal authority granted to Speakers became more limited. Widely regarded as the most effective recent Speaker was Sam Rayburn of Texas, who served more years (1940–47, 1949–53, 1955–61) than any other Speaker. Newt Gingrich of Georgia (1995–98) sought to recentralize power in the Speaker's position. Nancy Pelosi of California (2007–10) was the first woman to hold this post.

Other important leaders of the House are the majority and minority floor leaders and their deputies, the majority and minority whips. Floor leaders are elected at the beginning of each new Congress by the members of their own parties. Their primary responsibilities are to set the agenda, to schedule the business of the House, and to facilitate the formation of legislative coalitions on individual bills and amendments. Traditionally, party discipline was not strictly enforced, and members often crossed party lines to support or oppose legislation. Since the late 20th century, parties have become more polarized and cross-party voting has become less common.

The most important decision-making units within the House are its committees. In 2015 the House had 20 standing committees; a permanent select committee on intelligence; a select committee to investigate the 2012 attack on the U.S. diplomatic mission in Benghazi, Libya; and 4 joint committees (with the U.S. Senate). These panels had various subcommittees that handled most of the initial work of studying and drafting legislation. Members are assigned to committees by their parties, and the partisan division on each such body usually reflects the party ratio within the House as a whole.

For most of the 20th century, the House followed the rule of seniority in selecting committee chairpersons—that is, the member of the majority party with the longest continuous service on each committee automatically became its chairperson. The Democrats modified this system in the early 1970s; all majority party members were permitted to participate by secret ballot in selecting committee chairpersons. After Republicans became the majority party in 1995, they set term limits for committee chairpersons at 6 years, and in 2001, 13 House committees gained new leaders. The Democrats have not adopted that rule, which they see as undermining institutional memory.

The House establishes the rules of its own proceedings at the beginning of each new Congress. The Speaker, as presiding officer, is the principal arbiter of the rules and is assisted by the House parliamentarian, who is an appointed official. A majority of the members may overrule the Speaker's interpretations or applications of the procedural rules.

Any member of the House may introduce legislation, usually called a bill. Bills are referred to appropriate committees by the Speaker, following precedent. Committees and subcommittees hold public hearings on some bills and prepare them for consideration by the full House. Debate on the House floor is regulated by the Committee on Rules, which recommends the length of time to be devoted to each bill and the conditions under which amendments may be considered. The recommendations of the Committee on Rules must be approved by the full House before a bill is debated. At the close of the time allotted for debate and amendment, the full House votes on a bill, usually by a recorded roll call.

The House of Representatives has three primary responsibilities: to make laws, to serve as a representative assembly, and to oversee the administration of public policy. Legislative duties are shared with the Senate and with the president of the United States. All bills passed by the House require the concurrence of the Senate and the signature of the president (or an override of the president's veto by both houses) before becoming law. The Constitution also assigns several unique responsibilities to the House. All revenue-raising bills must originate in the House, although they become law only after action by both the Senate and the president. If no candidate for the presidency receives a majority of the electoral votes, the House is charged with choosing a president from among the three candidates with the most electoral votes. The House may initiate impeachment proceedings against a president or other federal officer by passing a bill of impeachment. Impeached officials are tried in the Senate. Only two presidents have been impeached: Andrew Johnson in 1868 and Bill Clinton in 1998; both were acquitted by the Senate.

Members of the House spend much time attending to their duties as representatives of the people in their districts. They frequently travel between Washington, D.C., and their districts, and they often meet with constituents visiting in Washington. Personal staffs assist them in answering mail, attending to constituent problems, and developing legislative proposals to provide benefits and relief to the people they represent. (In the 2000s, bills designed to benefit a specific district, known as "earmarks" or "pork-barrel legislation," have been discouraged.)

With the growth in the size of the federal government during the middle decades of the 20th century, the House had to devote more and more time to overseeing federal policies and programs. The enormous range of federal activities, and the natural resistance of both executive agencies and program beneficiaries to congressional scrutiny, make this responsibility difficult to fulfill. The House, nonetheless, has attempted to keep pace with its increased responsibilities by creating a number of oversight subcommittees and by vastly expanding its staff and information-support resources.