2021–22 Boston Celtics season

The 2021–22 Boston Celtics season was the 76th season of the franchise in the National Basketball Association (NBA). Following the Celtics' first-round exit to the Brooklyn Nets in five games from the previous season, Danny Ainge retired from his role as General Manager, and Brad Stevens was promoted to be the next President of Basketball Operations. The Celtics then hired Brooklyn Nets assistant Ime Udoka as the next head coach on June 28, 2021, in what was his only season as head coach before being suspended for violating team rules in September 2022 and later being replaced midway through the 2022–23 season.

The Celtics began the season with an 18–21 record but began a turnaround in January and finished with a 51–31 record and the #2-seed in the Eastern Conference. With the Portland Trail Blazers missing the playoffs for the first time since 2013, the Celtics now hold the longest active playoff streak, with consecutive appearances since 2015. They won the Atlantic Division for the first time since 2017. Multiple Celtics received NBA honors during the season. Jayson Tatum was selected to the All-NBA First Team and was named Eastern Conference Finals MVP, while Marcus Smart was named NBA Defensive Player of the Year and Robert Williams III joined him on the NBA All-Defensive Team.

In the first round of the playoffs, the Celtics swept the Brooklyn Nets in four games, which was their third series sweep in four seasons. In the second round, they faced the defending champion Milwaukee Bucks for the third time in five seasons and defeated them in seven games. In the final game of the series, the Celtics made 22 3-pointers, a record for the most ever in a Game 7. The Celtics then advanced to the Eastern Conference Finals for the fourth time in six years to face the top-seeded Miami Heat. In the previous two Conference finals matchups between the two teams, the Celtics lost both times: in 2012 in seven games and in 2020 in six. This time, they beat the Heat in seven games—including three wins on the road—to advance to the 2022 NBA Finals, their first Finals appearance since 2010. The Celtics faced the Golden State Warriors in a rematch of the 1964 Finals in an attempt to win their 18th championship and first since 2008, but lost in six games despite taking a 2–1 lead.