Constitutional law: Government structure - Legislative branch (Part 1 of 2)

The United States Congress or U.S. Congress is the bicameral legislature of the federal government of the United States and consists of the House of Representatives and the Senate. The Congress meets in the United States Capitol in Washington, D.C. Both senators and representatives are chosen through direct election, though vacancies in the Senate may be filled by a governor's appointment. Congress has 535 voting members: 100 senators and 435 representatives, the latter defined by the Reapportionment Act of 1929. In addition, the House of Representatives has six non-voting members, bringing the total membership of the US Congress to 541 or fewer in the case of vacancies.

The sitting of a congress is for a two-year term, at present beginning every other January; the current congress is the 116th. Elections are held every even-numbered year on Election Day. The members of the House of Representatives are elected for the two-year term of a congress representing the people of a single constituency, known as a district. Congressional districts are apportioned to states by population using the United States Census results, provided that each state has at least one congressional representative. Each state, regardless of population or size, has two senators. Currently, there are 100 senators representing the 50 states. Each senator is elected at-large in their state for a six-year term, with terms staggered, so every two years approximately one-third of the Senate is up for election.

Article One of the United States Constitution requires that members of Congress must be at least 25 years old (House) or 30 years old (Senate), have been a citizen of the United States for seven (House) or nine (Senate) years, and be an inhabitant of the state which they represent. Members in both chambers may stand for re-election an unlimited number of times.

The Congress was created by the Constitution of the United States and first met in 1789, replacing in its legislative function the Congress of the Confederation. Although not legally mandated, in practice since the 19th century, Congress members are typically affiliated with one of the two major parties, the Republican Party or the Democratic Party and only rarely with a third party or independents.