The United States Congress is the bicameral legislature of the federal government of the United States, consisting of the Senate, its upper house, and the House of Representatives, its lower house. Congress meets in the Capitol in Washington, D.C. Both representatives and senators are chosen through direct election. There are 535 voting Members of Congress; the House of Representatives has a membership of 435 and the Senate has a membership of 100. Members of the House of Representatives serve two-year terms representing the people of a district. Congressional districts are apportioned to states by population using the United States Census results, each state in the union having at least one representative in the Congress. Regardless of population, each of the 50 states has two senators; the 100 senators each serve a six-year term. The terms are staggered so every two years approximately one-third of the Senate is up for election. Most incumbents seek re-election, and their historical likelihood of winning subsequent elections exceeds 90 percent.