By their nature, filibusters elevate visibility of the issue at hand and have, as a by-product, the potential to inspire compromise. A final vote can only be taken if 60 Senators agree; this is called a vote of cloture (vote to end the filibuster).
According to the US Senate website, the word filibuster -- derived from a Dutch word meaning "pirate" -- was first used more than 150 years ago to describe "efforts to hold the Senate floor in order to prevent action on a bill."
The filibuster is related to "cloture," a rule adopted almost 100 years ago requiring a two-thirds vote. At times this was two-thirds of those voting; for a limited time, it was two-thirds of membership.
In 1975, the Senate reduced the number of votes needed to invoke cloture to three-fifths (60) of Senate membership. At the same time, they made the filibuster "invisible" by requiring only that 41 Senators state that they intend to filibuster; critics say this makes the modern filibuster "painless."
- 1841: Henry Clay "threatened to change Senate rules to allow the majority to close debate" when Democrats blocked a bank bill.
- 1872: Vice President Colfax ruled that "under the practice of the Senate the presiding officer could not restrain a Senator in remarks which the Senator considers pertinent to the pending issue."
- 1919: First use of Rule 22 when Senate invoked cloture to end debate against the Treaty of Versailles.
- 1935: Huey Long (LA) filibustered for 15 hours and 30 minutes trying, without success, to keep Senatorial oversight of National Recovery Administration's senior employees.
- 1957: Strom Thurmond (SC) set a filibuster record -- 24 hours and 18 minutes -- part of a move that successfully blocked the Civil Rights Act of 1957.
- 1964: Robert Byrd (WVA) filibustered for 14 hours and 13 minutes in an unsuccessful attempt to block the Civil Rights Act of 1964.
- 1968: The Abe Fortas appointment to succeed Earl Warren as Chief Justice of the Supreme Court was derailed by Republicans through filibuster.
- 2000: Majority Leader Bill First voted against cloture (85-14) on the Richard Paez nomination to the Ninth Circuit; he was confirmed ( 59-39).
The filibuster is only one way that Senators can block a vote. For example, the party in power can bottle up a bill or nomination in Committee, thus keeping it from coming to the floor for a vote.
The Senate has a process in place for amending rules; this process requires a two-thirds  vote. According to Congressional Quarterly, from 1919-1971, there were nine filibusters relating to Rule 22; in each case, there were insufficient votes to invoke cloture.
In 2005, then Senate Majority Leader Bill Frist threatened to end Democratic filibuster of judicial nominees by something called the "nuclear option." It is actually a series of steps designed to bypass the two-thirds vote requirement to change rules: (cite)
- The Senate moves to vote on a controversial nominee.
- At least 41 Senators call for filibuster.
- The Senate Majority Leader raises a point of order, saying debate has gone on long enough and that a vote must be taken within a certain time frame. (Current Senate rules requires a cloture vote at this point.)
- The Vice President -- acting as presiding officer -- sustains the point of order.
- A Democratic Senator appeals the decision.
- A Republican Senator moves to table the motion on the floor (the appeal).
- This vote - to table the appeal - is procedural and cannot be subjected to a filibuster; it requires only a majority vote (in case of a tie, the Vice President casts the tie-breaking vote).
- With debate ended, the Senate would vote on the issue at hand; this vote requires only a majority of those voting. The filibuster has effectively been closed with a majority vote instead of a three-fifths vote.