filibuster, term used to designate obstructionist tactics in legislative assemblies. It has particular reference to the U.S. Senate, where the tradition of unlimited debate is very strong. It was not until 1917 that the Senate provided for cloture (i.e., the ending of the debate) by a vote of two thirds of the Senators present. Yet, despite many attempts, cloture has been applied only rarely. The filibuster has been used by various blocs of Senators for different purposes; for example, by conservatives resisting civil-rights legislation in the 1960s, and by liberals resisting cuts in the capital gains tax in 1991. Attempts to reduce the cloture requirement have not been successful, partly because of the reluctance of the Senate to interfere with the tradition of free debate, which includes the right to speak on anything, however irrelevant, simply to keep the floor. In the 17th cent. the term was applied to buccaneers who plundered the Spanish colonies in the New World. In the 19th cent. the word was used more in reference to adventurers who organized and led, under private initiative, armed expeditions into countries with which the country from which they set out was at peace. Complications between the governments involved were likely to result. There was a series of filibustering expeditions from the United States against Cuba, Mexico, and Central and South American countries in the 19th cent., some of them led by citizens of the United States, as those of John A. Quitman and William Walker, and some by rebellious citizens of the government they sought to overthrow, as those of Narciso López against Cuba. Texas, when it was still part of Mexico, was the scene of many such filibustering activities.

Tactic of delaying action on a bill by talking long enough to wear down the majority in order to win concessions or force withdrawal of the bill. The tactic is normally employed by a group that cannot muster enough votes to defeat a bill by vote. Filibustering is possible in the U.S. Senate because Senate rules allow unlimited debate on a bill. A filibuster may be carried out by a group or a single member, and the speech need not be related to the bill under discussion. Calling for a vote to limit debate (cloture)—which requires 60 votes, the votes of three-fifths of the entire membership, in the U.S. Senate—or holding around-the-clock sessions to tire the speakers are measures used to defeat filibusters.

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