The United States Senate is the upper chamber of the bicameral Congress of the United States, the other being the House of Representatives. Established by Article I of the Constitution and first convened on 4 March 1789, the Senate consists of 100 members - two senators from each of the 50 states - serving staggered six-year terms. Senators are elected by popular vote within their states, a practice established by the Seventeenth Amendment (1913), which replaced the original method of selection by state legislatures. The Senate shares legislative power with the House but holds exclusive authority over ratifying treaties, confirming presidential appointments to the executive and judicial branches, and conducting impeachment trials of federal officeholders.

Each state elects two senators regardless of population, giving smaller states equal weight with larger ones in the upper chamber - a structural choice that reflects the Senate's origins in the Connecticut Compromise of 1787. Senators must be at least 30 years old, U.S. citizens for at least nine years, and residents of the state they represent. The Vice President of the United States serves as President of the Senate and may cast a tie-breaking vote, though the chamber typically operates under the leadership of the President pro tempore and party caucus leadership.

The Senate operates under procedural rules that distinguish it sharply from the House. The filibuster - a tactic allowing members to extend debate indefinitely and thereby delay or block a vote - has no counterpart in the House. Cloture, requiring a three-fifths majority (60 votes), is the primary mechanism for ending a filibuster on most legislation. Senate rules also allow for unanimous consent agreements and holds, giving individual members significant procedural leverage. The filibuster and cloture thresholds have been subjects of ongoing debate over their effect on legislative function. See Filibuster - Debate.

Confirmation of presidential nominees - including Cabinet secretaries, federal judges, and ambassadors - is a core Senate function. The confirmation process, including the threshold required for judicial nominees, has been a point of substantial political conflict, particularly following rule changes in 2013 and 2017 that eliminated the 60-vote cloture requirement for executive and non-Supreme-Court judicial nominees, and Supreme Court nominees, respectively.

Senate seats are distributed among political parties based on statewide elections held on a rolling basis, with roughly one-third of seats up for election every two years. The party holding the majority organizes the chamber, controls committee chairmanships, and sets the legislative agenda. A 50-50 split, which has occurred, is broken by the Vice President's party affiliation. Party discipline, caucus organization, and the role of the majority leader have grown significantly over the twentieth and twenty-first centuries.

The Senate's role, composition, and procedural norms have evolved substantially since 1789. For a detailed account, see United States Senate - History.

The Senate's design and procedures are subjects of active debate across the political spectrum.

• Equal state representation is undemocratic - Critics argue that equal representation regardless of population gives disproportionate political power to small states and dilutes the votes of citizens in large ones. See Equal State Representation Is Undemocratic - Viewpoint-viewpoint.

• Equal state representation protects federalism - Defenders argue that the Senate's structure was a deliberate and essential feature of the constitutional order, protecting state sovereignty and preventing majoritarian domination by large population centers. See Equal State Representation Protects Federalism - Viewpoint-viewpoint.

• The filibuster preserves deliberation and minority rights - Supporters contend that the filibuster forces consensus-building and protects against narrow majorities enacting sweeping legislation. See Filibuster Preserves Deliberation - Viewpoint-viewpoint.

• The filibuster obstructs representative governance - Critics hold that the filibuster has been used to block legislation supported by majorities of Americans and functions as a structural veto for minority factions. See Filibuster Obstructs Governance - Viewpoint-viewpoint.

• Senate confirmation has become excessively politicized - Some analysts argue that the confirmation process for executive and judicial nominees has deteriorated into partisan combat, degrading institutional norms. See Confirmation Is Excessively Politicized - Viewpoint-viewpoint.

• United States Senate - History
• Filibuster - Debate
• Senate Confirmation - Debate
• United States Congress
• United States House of Representatives
• Connecticut (Great) Compromise
• Seventeenth Amendment
• United States Constitution

1. U.S. Const. art. I, §§ 1-3.
2. U.S. Const. amend. XVII.
3. U.S. Senate, “Senate History: First Meeting of the Senate,” U.S. Senate Historical Office, https://www.senate.gov/artandhistory/history/common/briefing/Senate_First_Meeting.htm
4. U.S. Senate, “Filibuster and Cloture,” U.S. Senate Historical Office, https://www.senate.gov/artandhistory/history/common/briefing/Filibuster_Cloture.htm
5. U.S. Senate, “Qualifications,” https://www.senate.gov/senators/qualifications.htm
6. Congressional Research Service, “Senate Proceedings Determining Quorum,” updated periodically, https://crsreports.congress.gov