It takes 60 votes in the Senate to block or end a filibuster. Senate rules allow any member or group of senators to speak as long as necessary on an issue. The only way to end the debate is to evoke "cloture," or with a vote of 60 members. Without the 60 votes needed, the filibuster can go on indefinitely.
However, unlike filibusters throughout history, most filibusters today are not considered "talking filibusters."  The scene with Jimmy Stewart in Mr. Smith Goes to Washington is a famous example of a talking filibuster, where Smith’s character collapses after a 24-hour filibuster in the 1939 film.
In the current Senate, a member doesn’t need to speak on the floor, in a filibuster, to block a vote from happening. The filibuster can even be done by email. According to the current Senate rules, the minority or opposing party can indicate that is has 41 out of 100 voters that will support a filibuster by defeating a vote to block it. The majority party then needs to get 60 votes together to approve a time limit for a debate about the bill.
So a senator is not required to physically jump up and rant in public for hours to prevent a bill from passing. That senator just needs to issue a warning that there are enough votes to support a filibuster.
On March 6, 2013, Senator Rand Paul (R) led a 13-hour filibuster of President Obama's CIA Director nominee, John Brennan. Paul started the filibuster in order to highlight his concerns about the administration's drone policies. In particular, Paul said he was concerned about whether a drone could be used to kill an American citizen within the United States border, without any due process involved. Paul and other civil liberties activists have been critical that President Obama did not offer a clear response to the question. A total of 14 senators joined Paul in the filibuster -- 13 Republicans and one Democrat.
The day after the filibuster, Attorney General Eric Holder sent a letter to Paul, responding to the filibuster. Holder wrote, "Does the president have the authority to use a weaponized drone to kill an American not engaged in combat on U.S. soil? The answer to that is no."
McConnell filibusters his own bill
On December 6, 2012, another milestone in filibuster history was reached when Senator Mitch McConnell (R), became the first senator to filibuster his own proposal. McConnell did not give a lengthy speech, instead merely invoking the rules of filibuster on his bill to raise the passage threshold to 60 votes.
- United States Senate "Definitions and Glossary: Filibuster" Accessed March 7, 2013
- About.com "What is a Filibuster" Accessed March 7, 2013
- United States Senate "Filibuster Cloture" Accessed March 7, 2013
- Constitution Center "Fascinating Facts about Senate Filibusters" Accessed March 7,2013
- Washington Post "The Silent Filibuster Explained" Accessed March 7, 2013
- CNN "Rand Paul says he's heard from White House after filibuster," March 7, 2013
- USA Today "Rand Paul filibuster ranks among Senate's longest," March 7, 2013
- ABC News "Rand Paul Wins Applause From GOP and Liberals," March 7, 2013
- Washington Post "Eric Holder responds to Rand Paul with ‘no’," March 7, 2013
- Christian Science Monitor "Debt ceiling debate twist: Sen. Mitch McConnell filibusters himself" Accessed March 7, 2013
- Global Post "Mitch McConnell filibusters himself after Dems call bluff" Accessed March 7, 2013