The 2011 NBA lockout was the fourth and most recent lockout in the history of the National Basketball Association (NBA). Team owners began the work stoppage upon expiration of the 2005 collective bargaining agreement (CBA). The 161-day lockout began on July 1, 2011, and ended on December 8, 2011. It delayed the start of the 2011–12 regular season from November to December, and it reduced the regular season from 82 to 66 games. The previous lockout in 1998–99 had shortened the season to 50 games. During the lockout, teams could not trade, sign, or contact players. Players additionally did not have access to NBA team facilities, trainers, or staff.

Negotiations between the owners, led by league commissioner David Stern, and the players, headed by director Billy Hunter and president Derek Fisher of the labor union National Basketball Players Association (NBPA), began in early 2011 and continued through November. The main issues dividing both sides were the division of revenue, the structure of the salary cap and luxury tax. Owners proposed to reduce the players' share of basketball related income (BRI) from 57% to 47%, but the players countered with 53% of BRI. Owners wanted to implement a hard salary cap and a harsher luxury tax, hoping to increase competition among teams, whereas players wanted to keep the current soft salary cap structure intact.

As both sides failed to reach an agreement, the NBA canceled the preseason and all games through December. On November 14, the players dissolved the union, allowing them to file antitrust lawsuits against the league. On November 26, both sides reached a tentative agreement to end the lockout. The new CBA calls for a revenue split of 49-to-51.2% and a flexible salary cap structure with harsher luxury tax. After the tentative deal was reached, owners allowed players to have voluntary workouts at team sites starting December 1. After the deal was ratified on December 8, training camps, trades, and free agency began the next day. During the lockout, some players signed contracts to play in other countries, mostly in Europe and Asia, with most of them having the option to return upon the lockout's conclusion. The lockout also affected the economy outside the league due largely to cities that had teams in the league losing revenue generated by games as well as television networks that broadcast the league losing ratings and advertisement revenue due to games not being played.

After the previous lockout, which shortened the 1998–99 season from 82 to 50 games, a six-year deal between the owners, led by commissioner David Stern, and the players, led by director Billy Hunter and president Patrick Ewing of the labor union National Basketball Players Association (NBPA), was reached. As the CBA was set to expire on June 30, 2005, the two sides began to negotiate in early 2005. There were several issues obstructing the new agreement, which included adding an age limit for rookies, toughening the existing drug-testing program and limiting the length of long-term contracts. However, negotiations went smoothly and the two sides were able to reach a deal in June 2005, avoiding the lockout. That deal guaranteed players 57% of basketball-related income (BRI) and lasted for six years, until June 30, 2011. A year after signing the deal, eight owners signed a petition requesting Stern address the disparity between small-market and large-market teams. They wrote that "the hard truth is that our current economic system works only for larger-market teams and a few teams that have extraordinary success ...The rest of us are looking at significant and unacceptable annual financial losses."

Derek Fisher succeeded Ewing as NBPA president in 2006. In early 2011, negotiations on a new CBA began. The league claimed that it was losing $300 million a year (22 out of 30 teams were losing money last season) and proposed to reduce 40% of players' salary (about $800 million) and institute a hard salary cap (at $45 million per team) as opposed to a soft cap (at $58 million) currently in use. The union disputed those figures and steadfastly opposed those changes. Hunter said that he was advising players to prepare for a lockout. In May 2011, the NBPA filed a complaint with the National Labor Relations Board (NLRB), accusing the league of negotiating in bad faith by failing to provide critical financial data to the union and repeatedly threatening to lock out players. The NBA quickly rejected the complaint, saying that the league complies fully with federal labor laws. The union also considered the option of decertification, which allows players to file an antitrust lawsuit against the NBA.

With time winding down, negotiations continued in May and June. On the salary cap, the owners, in their newest proposal, call for a system called the "flex cap" that limits payroll at $62 million but penalizes teams if the teams payroll exceeds the league's average payroll of that season. The union argued that it is still a hard cap because the ceiling would kick in eventually. On salary reduction, players offered to cut $500 million over the next five years (their share of BRI would be reduced from 57 to 54.3 percent). The owners instead proposed to cut $2 billion over the next 10 years.

As a last-ditch effort to avert a lockout, owners and players met again on June 30, 2011, to negotiate, but both sides failed to reach a resolution on key issues like salary cap and BRI splits. Both Stern and Hunter said that the two sides remained far apart. The owners demanded a larger share, claiming that they were losing money. The players, on the other hand, were willing to make concessions, but they refused to completely cave in to owners' demands. Negotiations broke off, and the CBA expired at midnight.

The lockout was officially started by the owners on July 1, 2011, during which teams could not trade, sign, or contact players, and players could not access NBA team facilities, trainers, or staffs. Negotiations resumed at an August 1 bargaining session, but it fell apart after three hours. On August 2, 2011, the NBA filed two unfair labor practice claims against the NBPA, one at the NLRB and another at a federal district court in New York. The league accused the players of being uncooperative in negotiations by threatening to dissolve their union and file antitrust lawsuits. Hunter, in a statement released by the union, called the lawsuits "without merit" and that the union would seek to dismiss it in court. On August 4, Hunter said that he thought the entire 2011–12 season would likely be canceled.