A filibuster is a political procedure in which one or more members of a legislative body prolong debate, or threaten to prolong debate on a legislative measure, so as to delay or prevent a vote being taken.

In the United States, the filibuster is typically associated with the U.S. Senate, which traditionally allowed for any Senator to speak for an unlimited time on any measure. In 1917, the Senate revised its rules to allow a two-thirds majority to end a filibuster, a procedure known as “cloture.” In 1975, the cloture threshold was lowered to 60 votes. A Democratic majority eliminated the filibuster for judicial nominees below the Supreme Court in 2013 and a Republican majority eliminated the filibuster for Supreme Court nominees in 2019.

While historically the filibuster was used only rarely in the U.S. Senate, in recent decades, both parties have routinely threatened filibusters on almost all major legislation. This has meant that in practice, a supermajority of 60 Senators is needed to pass a cloture motion and advance most bills through the Senate. The only major exception, besides judicial nominees, are budget reconciliation bills, which are exempt from the filibuster and thus need only a simple majority of 51 Senators to pass.

The filibuster is seen by critics as contrary to the principle of majority rule and responsible for the inability of Congress to address major problems, while defenders see it as a vital protection of the rights of the minority and as a hallowed Senate tradition. In recent years, both parties have threatened to abolish the filibuster while in the majority, but attempts to do so have failed to muster the necessary 51-vote majority.

Oklahoma is among the 37 states that does not have a filibuster; the majority party in each chamber determines the length of time allowed for debate on each measure before it is brought up for a vote.