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 gubernatorial appointment. Congress has 535 voting members: 435 Representatives and 100 Senators. The House of Representatives has six non-voting members representing Puerto Rico, American Samoa, Guam, the Northern Mariana Islands, the U.S. Virgin Islands, and Washington, D.C. in addition to its 435 voting members. Although they cannot vote, these members can sit on congressional committees and introduce legislation.
The members of the House of Representatives serve two-year terms 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.