The United States Senate is the upper chamber of the United States Congress, with the House of Representatives being the lower chamber. Together they compose the national bicameral legislature of the United States.

The composition and powers of the Senate are established by Article One of the United States Constitution. The Senate is composed of senators, each of whom represents a single state in its entirety. Each of the 50 states is equally represented by two senators who serve staggered terms of six years, for a total of 100 senators. From 1789 to 1913, senators were appointed by legislatures of the states they represented. They have been elected by popular vote since the 1913 ratification of the Seventeenth Amendment.

As the upper chamber of Congress, the Senate has several powers of advice and consent which are unique to it. These include the approval of treaties, and the confirmation of Cabinet secretaries, federal judges (including Federal Supreme Court justices), flag officers, regulatory officials, ambassadors, other federal executive officials and federal uniformed officers. If no candidate receives a majority of electors for vice president, the duty falls to the Senate to elect one of the top two recipients of electors for that office. The Senate conducts trials of those impeached by the House. The Senate has typically been considered both a more deliberative and prestigious body than the House of Representatives due to its longer terms, smaller size, and statewide constituencies, which historically led to a more collegial and less partisan atmosphere.

The Senate chamber is located in the north wing of the Capitol Building in Washington, D.C. The vice president of the United States serves as presiding officer and president of the Senate by virtue of that office, despite not being a senator, and has a vote only if the Senate is equally divided. In the vice president's absence, the president pro tempore, who is traditionally the senior member of the party holding a majority of seats, presides over the Senate. In the early 1920s, the practice of majority and minority parties electing their floor leaders began. The Senate's legislative and executive business is managed and scheduled by the Senate majority leader.