The United States Senate is the upper house of the bicameral United States Congress, the lower house being the House of Representatives (the United States Constitution does not use these terms, however).

In the Senate, each state is represented by two members. Membership is therefore based on the equal representation of each state, regardless of population, for a total membership of 100. Senators serve six-year terms that are staggered so elections are held for a third of the seats (a class) every second year.

The Senate is regarded as a more deliberative body than the House of Representatives; the Senate is smaller and its members serve longer terms, allowing for a more collegial and less partisan atmosphere that is somewhat more insulated from public opinion than the House. The Senate has several exclusive powers enumerated in Article One of the Constitution not granted to the House; most significantly, the President cannot ratify treaties or, with rare exception, make important appointments — most significantly ambassadors, members of the federal judiciary (including the Supreme Court), governors of the Federal Reserve and members of the Cabinet — without the advice and consent of the Senate.