2009–10 Cleveland Cavaliers season

The 2009–10 Cleveland Cavaliers season was the 40th season of the franchise in the National Basketball Association (NBA). The Cavaliers finished with the best record in the NBA at 61–21, earning them first place in the East. The season saw LeBron James win the MVP Award for the second straight year. The Cavaliers had the fifth best team offensive rating in the NBA.

After defeating the Derrick Rose-led Chicago Bulls in the first round in five games, the Cavs faced the 4th-seeded Boston Celtics in the Semifinals in a rematch of the 2008 Conference semifinals where the Celtics won in seven games. The Cavaliers were favored to beat them, but lost in six games despite being up 2-1. The Celtics would advance to the NBA Finals and lose to the Los Angeles Lakers in seven games. Following the season, Danny Ferry stepped down as general manager, head coach Mike Brown was fired, and James signed as a free agent with the Miami Heat, but would return to the Cavaliers in 2014, Shaquille O'Neal signed as a free agent with the Boston Celtics, which turned out to be O'Neal's final season as a player, and Zydrunas Ilgauskas also left the team to join one season with the Heat before retiring.

After LeBron's departure, the Cavaliers struggled greatly without him for four seasons, and entered a state of rebuilding. The Cavaliers would not make the playoffs again until 2015, when LeBron returned to the Cavaliers, who drafted All-Star Kyrie Irving and traded for All-Star Kevin Love.

As of 2023, this was the last time that the Cavaliers have won 60 or more games. This was also the last time that LeBron lost in the playoffs before the Finals until 2021 when the Los Angeles Lakers lost to the Phoenix Suns in six games in the first round, which was also the first time in James' career that he exited in the first round.