The 2009–10 NBA season was the 64th season of the National Basketball Association (NBA). The 1,230-game regular season (82 games for each of the 30 teams) began on Tuesday, October 27, 2009, and ended on Wednesday, April 14, 2010.
The 2009 NBA draft was held on June 25, 2009, and Blake Griffin was selected first overall by the Los Angeles Clippers. The Dallas Mavericks hosted the 59th Annual All-Star Game at Cowboys Stadium in Arlington, Texas, on February 14, 2010.
For the second time in NBA history, all eight Western Conference playoff teams won at least 50 games, and only 7 wins separated the Western Conference #1 seed from #8 seed. Both of these events first occurred in 2008.
Cleveland's league-leading 61 wins was the lowest win total to lead the league since the Indiana Pacers won 61 games in 2003–04.
The New Jersey Nets became the fifth team in NBA history to lose 70 games in a season.
* On October 1, the pre-season games started and were refereed by replacement referees from the Women's National Basketball Association (WNBA) and the NBA D-League due to the lockout of referees. This marked the first time that replacement referees were used in the NBA since the 1995–96 season.
* On October 2, the NBA Board of Governors approved the expanded use of instant replay starting this season to determine whether a 24-second shot clock violation occurred during a play, and to determine during the last two minutes of regulation play or any overtime period which player last touched the ball prior to it going out-of-bounds.
* On October 8, the NBA played its first-ever game in Taipei. A pre-season game between the Indiana Pacers and the Denver Nuggets was played at Taipei Arena. Taipei became the seventh Asian city to host an NBA game, after Beijing, Guangzhou, Macau, Shanghai, Tokyo and Yokohama.
* On October 9, Marvin Fishman, one of the original owners of the Milwaukee Bucks, died at the age of 84.
* On October 23, the NBA and its referees announced that they have agreed on a new labor agreement for the next two seasons, thus ending the lockout of referees.
* On October 27, the regular season opened with a record of 83 international players on the opening night rosters, tying the records set in the 2006–07 season. Israeli Omri Casspi, Swede Jonas Jerebko and Tanzanian Hasheem Thabeet were representing their countries for the first time in the NBA. The opening night rosters also featured a record number of former D-League players with 63 players on 29 NBA teams.
* On November 10, Hall of Famer coach Al Cervi died at the age of 92.
* On November 24, Washington Wizards owner Abe Pollin died at the age of 85.
* On November 25, ten-time All-Star Allen Iverson announced his retirement from the NBA. He was waived by the Memphis Grizzlies on November 19 after playing three games.
* On January 6, Washington Wizards guard Gilbert Arenas was suspended indefinitely, pending further investigation of his admission of bringing guns to the Wizards' locker room. Reports said that Arenas brought his gun because of a dispute with teammate Javaris Crittenton over a gambling debt. Arenas was later charged with carrying a gun without a license and pleaded guilty to the charge.
* On January 9, Detroit Pistons guard Ben Gordon scored the 10 millionth point in NBA regular season history.
* On January 27, the NBA suspended Washington Wizards guards Gilbert Arenas and Javaris Crittenton for the rest of the season. Both Arenas and Crittenton brought guns into the team's locker room at Verizon Center, a violation of both the league's constitution and of the city's laws requiring any guns in the city be licensed in Washington and kept in the home. A few days earlier, Crittenton was also charged with, and pleaded guilty to, a misdemeanor count of possession of an unregistered firearm