The United States legislature is divided into two chambers: the House of Representatives and the Senate. Senators are elected to six-year terms. Members of the House of Representatives -- called representatives, congressmen, congresswomen or members of Congress -- are elected to two year terms. The length of representatives' terms is stipulated by Article I, Section 2 of the U.S. Constitution.

Even-Numbered Years

Members of the U.S. House of Representatives are elected directly by the people in the districts they represent. Districts are drawn up according to population. The average district represents about 600,000 people, though every state is guaranteed at least one congressional district regardless of population. Elections for representatives are held every even numbered year.

Extraordinary Vacancies

When a congressional seat is vacated due to death, resignation, impeachment or other extraordinary circumstances, a special election may be called by the district's state governor or the seat may be left vacant until the next general election. If the vacancy occurs during the first year of the congressional term, the governor must hold a special election. When a special election is called, the newly elected representative fulfills the remainder of the two-year term; the position is up for election again in the next general election.