BOS Celtics

The Boston Celtics were formed on June 6, 1946, by Boston Garden-Arena Corporation president Walter A. Brown as a team in the Basketball Association of America. In 1948, the team earned its first playoff appearance, only to lose to the Chicago Stags 4–1. In 1949, the team missed the playoffs, fifth in the Eastern Division. Then, on August 3, 1949, the team became part of the National Basketball Association following the merger of the BAA and rival National Basketball League. In 1950, the Celtics signed Chuck Cooper, becoming the first NBA franchise to draft a black player. Chuck Connors of The Rifleman fame was an original member of the Celtics in 1946.

The Celtics struggled during their early years, until the hiring of coach Red Auerbach. In the franchise's early days, Auerbach had no assistants, ran all the practices, did all the scouting—both of opposing teams and college draft prospects—and scheduled all road trips. One of the first great players to join the Celtics was Bob Cousy, whom Auerbach initially refused to draft out of nearby Holy Cross because he was "too flashy". Cousy's contract eventually became the property of the Chicago Stags, but when that franchise went bankrupt, Cousy went to the Celtics in a dispersal draft.

After the 1955–56 season, Auerbach made a stunning trade, sending perennial All-Star Ed Macauley to the St. Louis Hawks along with the draft rights to Cliff Hagan for the second overall pick in the draft. After negotiating with the Rochester Royals—a negotiation that included a promise that the Celtics owner would send the highly sought-after Ice Capades to Rochester if the Royals would let Russell slide to No. 2—Auerbach used the pick to select University of San Francisco center Bill Russell. Auerbach also acquired Holy Cross standout, and 1957 NBA Rookie of the Year, Tom Heinsohn. Both Russell and Heinsohn worked extraordinarily well with Cousy, and they were the players around whom Auerbach would build the champion Celtics for more than a decade. With Bill Russell, the Celtics advanced to the 1957 NBA Finals and defeated the St. Louis Hawks in seven games, earning their first NBA title. In 1958, the Celtics again advanced to the NBA Finals, this time losing to the Hawks in 6 games.

Following the acquisition of K.C. Jones in 1958, the Celtics began a dynasty that would last for more than a decade. In 1959, the Celtics won the NBA championship after sweeping the Minneapolis Lakers, the first of their record eight consecutive championships. During that time, the Celtics met the Lakers in the Finals five times, starting an intense and often bitter rivalry that has spanned generations. In 1964, the Celtics became the first NBA team to have an all African-American starting lineup. On December 26, 1964, Willie Naulls replaced an injured Tom Heinsohn, joining Tom 'Satch' Sanders, K.C. Jones, Sam Jones, and Bill Russell in the starting lineup. The Celtics defeated St. Louis 97–84. Boston won its next 11 games with Naulls starting in place of Heinsohn. The Celtics of the late 1950s–1960s are widely considered one of the most dominant teams of all time.

Auerbach retired as coach after the 1965–66 season and Russell took over as player-coach, which was Auerbach's ploy to keep Russell interested. With his appointment Russell became the first African-American coach in any U.S. pro sport. Auerbach would remain the general manager, a position he would hold well into the 1980s. However, the Celtics' string of NBA titles ended when they lost to the Philadelphia 76ers in the 1967 Eastern Conference Finals. The aging team managed two more championships in 1968 and 1969, defeating the Los Angeles Lakers each time. Russell retired after the 1969 season, effectively ending a Celtics dynasty that had garnered an unrivaled 11 NBA titles in 13 seasons. The team's run of 8 consecutive is the longest championship streak in U.S. professional sports history, with Russell's 11 titles being the most won by an NBA player.

The 1969–70 season was a rebuilding year, as the Celtics had their first losing record since the 1949–50 season. However, with the acquisition of Paul Silas and future Hall of Famers Dave Cowens and Jo Jo White, the Celtics soon became dominant again. After losing in the Eastern Conference Finals in 1972, the Celtics regrouped and came out determined in 1973 and posted an excellent 68–14 regular season record. But the season ended in disappointment, as they were upset in seven games by the New York Knicks in the Conference Finals. John Havlicek injured his right shoulder in game six and was forced to play game seven shooting left-handed. The Celtics returned to the playoffs the next year, defeating the Milwaukee Bucks in the 1974 NBA Finals for their 12th NBA championship. Boston took a 3–2 series lead and had a chance to claim the title on their home court. The Bucks won Game Six in Boston when Kareem Abdul-Jabbar nestled in a hook shot with 3 seconds left in the game's second overtime, and the series returned to Milwaukee. Cowens was the hero in Game 7, scoring 28 points, as the Celtics brought the title back to Boston for the first time in five years.

In 1976, the team won yet another championship, defeating the Phoenix Suns in six games. The Finals featured one of the greatest games in NBA history. With the series tied at two games apiece, the Suns trailed early in the Boston Garden, but came back to force overtime. In double overtime, a Gar Heard turn-around jumper at the top of the key sent the game to a third overtime, at which point the Celtics prevailed. After the 1976 championship and a playoff appearance in 1977, Boston went into another rebuilding phase. In the 1977 NBA draft, the Celtics drafted a young forward from UNC Charlotte named Cedric Maxwell. "Cornbread" Maxwell did not contribute much in his rookie season, but he showed promise. Auerbach's job became even tougher following the 1977–78 season in which they went 32–50 as Havlicek, the Celtics' all-time leading scorer, retired after 16 seasons.

The Celtics owned two of the top eight picks in the 1978 NBA draft. Auerbach took a risk by selecting junior Larry Bird of Indiana State with the sixth overall pick, knowing that Bird would stay in college for his senior year but believing that his potential would make him worth the wait. The team retained Bird's rights for one year and signed him soon after he led Indiana State to the NCAA championship game. In 1978, Celtics owner Irv Levin traded franchises with Buffalo Braves owner John Y. Brown Jr. Two weeks before the swap of franchises was made official, details of a six-player trade between the two teams were reported. Boston sent Freeman Williams, Kevin Kunnert, and Kermit Washington to the Braves for "Tiny" Archibald, Billy Knight, and Marvin Barnes. The move turned Boston fans against Brown, both because Kunnert and Washington were seen as key pieces of the team's future and because Auerbach publicly stated that he was not consulted about the trade.

The relationship between Brown and Auerbach worsened with Brown's decision to acquire Bob McAdoo in February 1979, in exchange for three first-round draft picks that Auerbach had planned to use to rebuild the franchise. Again, Brown made the trade without consulting Auerbach. Auerbach almost left Boston to take a job with the New York Knicks as a result. With public support strongly behind Auerbach, Brown sold the team to Harry Mangurian in 1979 rather than run the risk of losing his famed general manager. The Celtics would struggle through the season, going 29–53. Newcomers Chris Ford, Rick Robey, Cedric Maxwell and Nate Archibald failed to reverse the team's momentum.

Larry Bird debuted for the Celtics during the 1979–80 season. With a new owner in place, Auerbach made a number of moves that would bring the team back to prominence. He almost immediately traded McAdoo, a former NBA scoring champion, to the Detroit Pistons for guard M. L. Carr, a defensive specialist, and two first-round picks in the 1980 NBA draft. He also picked up point guard Gerald Henderson from the CBA. Carr, Archibald, Henderson and Ford formed a highly competent backcourt, blending in well with the talented frontcourt of Cowens, Maxwell and Bird. With Bird winning NBA Rookie of the Year honors the team went 61–21, a 32-game improvement from the previous season. Playing strong in the playoffs, the Celtics fell to the Philadelphia 76ers in the Eastern Conference Finals.

After the season, Auerbach completed one of the most lopsided trades in NBA history, garnering a pair of future Hall of Famers for a pair of first-round draft picks. Seeking to improve the team immediately, Auerbach sent the team's two first-round draft picks to the Golden State Warriors for both center Robert Parish and the Warriors' first-round pick. He then used the pick the Celtics obtained from Golden State to select University of Minnesota power forward Kevin McHale. The "Big Three" of Bird, McHale and Parish played together for the Celtics until 1992, won three NBA championships together, and were later described as the best NBA frontcourt of all time.

Despite losing center Dave Cowens to retirement late in training camp, the Celtics went 62–20 under coach Bill Fitch in 1980–81. Once again, the Celtics faced the 76ers in the Eastern Conference Finals, falling behind 3–1 before coming back to win Game Seven, 91–90. The Celtics went on to win the 1981 NBA championship over the Houston Rockets, with Maxwell being named NBA Finals MVP.

Following the 1981–82 season, the Celtics once again met the 76ers in the playoffs. This time, they lost in seven games. In 1983 the Celtics were swept in the playoffs (a first for the franchise) by the Milwaukee Bucks; afterwards, Fitch resigned and the team was sold to new owners led by Don Gaston.

In 1983–84, the Celtics under new coach K. C. Jones would go 62–20 and return to the NBA Finals after a three-year hiatus. Boston came back from a 2–1 deficit to defeat the Lakers for their 15th championship. Bird renewed his college rivalry with Lakers star Magic Johnson during this series. After the season, Auerbach officially retired as general manager, but maintained the position of team president. He was succeeded by Jan Volk.

In 1985, the Lakers and Celtics met again in the Finals, with the Lakers winning. This was the first time the Lakers had defeated the Celtics in the Finals and the only time the team had won a championship at Boston Garden. During the following off-season, the Celtics acquired Bill Walton from the Los Angeles Clippers in exchange for Cedric Maxwell. Walton had been an All-Star and league MVP while leading the Portland Trail Blazers to the 1977 NBA championship, but injuries had hobbled him since. Considered the best passing center in NBA history, he stayed healthy and was a big part of the Celtics' success in 1986.

The Celtics won the second pick in the 1986 NBA draft and drafted University of Maryland star Len Bias, one of the most heralded prospects of his era. Bias died 36 hours later of an accidental cocaine overdose. Despite the tragedy, the Celtics remained competitive in 1986–87, going 59–23 and again winning the Eastern Conference Championship. They were defeated in the Finals by the Lakers in six games.

In 1988, the Celtics lost in six games to the Detroit Pistons in the Eastern Conference Finals. Following the season, head coach K.C. Jones retired and was replaced by assistant Jimmy Rodgers. Boston's hopes for 1988–89 faded when Bird underwent a procedure to remove bone spurs in his feet early in the season, and the Celtics won just 42 games before a first-round playoff defeat to the Pistons. Bird returned in 1989–90 and led the Celtics to a 52–30 record. In the playoffs, the Celtics collapsed after winning the first two games in a best-of-five series against the New York Knicks, losing three straight games and the series. After the playoffs, Rodgers was fired and replaced by assistant coach and former Celtics player Chris Ford.

Under Ford's leadership, the Celtics improved to 56–26 in 1990–91, recapturing the Atlantic Division title even though Bird missed 22 games with several injuries. The Celtics again lost to the Pistons in the playoffs. In 1992, a late-season rally allowed a 51–31 Celtics team to catch the New York Knicks and repeat as Atlantic Division champions. After sweeping the Indiana Pacers in the first round, the Celtics lost a seven-game Eastern Conference Semifinals series to the Cleveland Cavaliers. Back injuries limited Bird to only 45 regular season games, and just four of ten in the playoffs. After thirteen NBA seasons and a gold medal at the Barcelona Olympics with the Dream Team, continued back trouble led Bird to retire in 1992.

The loss of Bird and the aging of the team's other veteran stars forced coach Chris Ford into rebuilding mode. Hopes centered on 26-year-old Reggie Lewis, a small forward out of Boston's Northeastern University. In the first round of the 1993 playoffs Lewis fainted during Boston's four-game series loss by the Charlotte Hornets. An examination revealed heart problems, but Lewis was able to get doctors to clear him for a comeback. Before he could make it he died of a heart attack while shooting baskets at Brandeis University during the off-season. The Celtics honored his memory by retiring his number 35. With McHale having retired after the Celtics' playoff loss to the Hornets, Boston's original Big 3 era came to an end in 1994 upon Robert Parish's signing with Charlotte. The team collapsed, finishing out of the playoffs with a 32–50 mark.

In 1994, the Celtics hired former player and legendary towel-waving cheerleader M. L. Carr as the team's new vice president of basketball operations. Working alongside general manager Jan Volk, Carr selected University of North Carolina star Eric Montross with Boston's first-round pick in the 1994 NBA draft. Montross became the new heir apparent in the paint, but failed to develop and was eventually traded. 1994–95 was the Celtics' final season in the Boston Garden. The Celtics signed aging Dominique Wilkins as a free agent, who led the team in scoring with 17.8 PPG. Second-year player Dino Rađa, a power forward from Croatia, added an interior presence the team had been lacking in 1993–94. The Celtics made the playoffs, losing to the heavily favored Orlando Magic in four games. In 1995, the Celtics moved from the Boston Garden to the Fleet Center (later TD BankNorth, then TD Garden). Carr fired Chris Ford and took the coaching reins himself. After drafting Providence College star Eric Williams, the Celtics struggled to a 33–49 record.

Things got worse in 1996–97 as the Celtics lost a franchise-record 67 games, setting an unwanted NBA record winning only once against other Atlantic Division teams and just fifteen victories overall. In spite of the emergence of 1st-round draft pick Antoine Walker, Carr resigned after the season ended, while Rick Pitino was hired to join the franchise as the team's president, director of basketball operations, and head coach, reportedly on a $70 million ten-year contract. Volk resigned on May 7, 1997. Pitino's appointment as team president was controversial as Auerbach, the incumbent who had filled that role for more than 25 years, first heard about the change from local media. Unfortunately for the franchise, Pitino was not the savior everyone hoped he would be. Auerbach bore the insult of being elbowed out with dignity, even as the team failed to improve.

The Celtics received the third and sixth draft picks in the 1997 NBA draft, and used the picks to select a brand new backcourt through Chauncey Billups and Ron Mercer. The young team that lost 67 games the year before was dismantled, with David Wesley, Dino Rađa and Rick Fox being let go, and Williams traded to the Denver Nuggets for a pair of second round draft picks (Williams would return to the Celtics in 1999 and played for four years). Walter McCarty was also acquired in a trade with the Knicks. With a promising start, upsetting the defending champions Chicago Bulls at home on opening night, and hard play from the youngsters that led to leaderships in turnovers and steals, the team improved its victories from 15 to 36 despite many losing streaks. Billups was subsequently traded to the Raptors during his rookie year, and Mercer was traded to the Nuggets during his third season.

The following year in the 1998 NBA draft, the Celtics drafted Paul Pierce, a college star who had been expected to be drafted much earlier than the Celtics' 10th overall pick. Pierce had an immediate impact during the lockout-shortened 1998–99 season, averaging 19.5 points and being named Rookie of The Month in February as he led the league in steals. However, the Celtics continued to struggle as Pitino failed to achieve meaningful success. After Boston lost to the Toronto Raptors on March 1, 2000, on a buzzer-beater by Vince Carter, Pitino delivered the memorable "walking through that door" speech, invoking Bird, McHale and Parish, which has been frequently cited over the years as a reality check for organizations wrestling with bygone glory. He resigned in January 2001.

Following the resignation of Rick Pitino, the Celtics saw modest improvement under coach Jim O'Brien. Paul Pierce matured into an NBA star and was ably complemented by Antoine Walker and the other players acquired over the years. While the team was 12–21 when Pitino left, O'Brien's record to finish the season was 24–24. Following the 2000–01 season O'Brien was given the job of head coach on a permanent basis. As a result of numerous trades, the Celtics had three picks in the 2001 NBA draft. They selected Joe Johnson, Joe Forte, and Kedrick Brown. Only Johnson managed to succeed in the NBA, becoming a perennial All-Star after leaving the Celtics.

The Celtics entered the 2001–02 season with low expectations. The team's success in the latter stages of 2000–01 was largely forgotten, and critics were surprised when the team, along with the New Jersey Nets, surged to the top of the Atlantic Division ahead of the Philadelphia 76ers, who were fresh off a trip to the NBA Finals. The Celtics won a hard-fought 5-game series with the 76ers in the first round, 3–2. Pierce scored 46 points in the series-clinching game at the Fleet Center. In the Conference Semifinals, the Celtics defeated the favored Detroit Pistons 4–1. In their first trip to the Eastern Conference Finals since 1988, the Celtics jumped out to a 2–1 series lead over the Nets, after rallying from 21 points down in the fourth quarter to win Game 3, but would lose the next three games to fall 4–2.

In 2003, the Celtics were sold by owner Paul Gaston to Boston Basketball Partners L.L.C., led by H. Irving Grousbeck, Wycliffe Grousbeck and Steve Pagliuca. The team made it back to the playoffs but were swept by the Nets in the second round, despite bringing Game 4 to double overtime. Before their elimination, the team hired former Celtics' guard Danny Ainge as general manager, moving Chris Wallace to another position in the organization. Ainge believed the team had reached its peak and promptly sent Antoine Walker to the Dallas Mavericks (along with Tony Delk). In return, the Celtics received the often-injured Raef LaFrentz, Chris Mills, Jiří Welsch, and a first-round pick in 2004. The Celtics made the playoffs, only to be swept in the first round by the Indiana Pacers, losing all four games.

The Celtics were a young team under new coach Doc Rivers during the 2004–05 season, having drafted youngsters Al Jefferson, Delonte West and Tony Allen in the 2004 Draft. Yet they seemed to have a core of good young players, led by Pierce and rookie Al Jefferson, to go along with a group of able veterans. The Celtics went 45–37 and won their first Atlantic Division title since 1991–92, receiving a boost from returning star Antoine Walker in mid-season. The Pacers defeated them in the first round yet again, with the series culminating in an embarrassing 27-point loss in Game 7 at the Fleet Center. After the season Walker was traded again, this time to the Miami Heat. Despite Pierce's career season, in which he averaged career-highs in points (26.8), the Celtics missed the playoffs with a 33–49 record, owing largely to a young roster and constant roster shuffling, which saw the likes of Marcus Banks, Ricky Davis and Mark Blount traded for underachieving former first-overall pick Michael Olowokandi and former all-star Wally Szczerbiak.

The Celtics continued to rebuild in the 2006 NBA draft. The Celtics selected Kentucky point guard Rajon Rondo, who was to become a key piece in the team's revival. In the second round the Celtics added center Leon Powe. The 2006–07 season was a gloomy one for the franchise, starting with the death of Red Auerbach at 89. Auerbach was one of the few remaining people who had been a part of the NBA since its inception in 1946. The Celtics went 2–22 from late December 2006 through early February 2007 after losing Pierce to injury, the result of a stress reaction in his left foot. At first, the Celtics received a much-needed boost from guard Tony Allen but he tore his ACL and MCL on a needless dunk attempt after the whistle. The Celtics compiled a record of 24–58, second-worst in the NBA, including a franchise-record 18-game losing streak. At the end of the season, the Celtics, with the second-worst record in the NBA, were at least hopeful that they could secure a high draft pick and select either Greg Oden or Kevin Durant to help rebuild the franchise, but the Celtics fell to fifth in the Draft Lottery.

In the summer of 2007, general manager Danny Ainge made a series of moves that returned the Celtics to prominence. On draft night, he traded No. 5 pick Jeff Green, Wally Szczerbiak and Delonte West to Seattle for perennial All-Star Ray Allen and Seattle's second-round pick, which the team used to select LSU's Glen "Big Baby" Davis. The Celtics then traded Ryan Gomes, Gerald Green, Al Jefferson, Theo Ratliff, Sebastian Telfair, and a first-round draft pick to the Timberwolves in exchange for superstar power forward Kevin Garnett. These moves created a new "Big Three" of Pierce, Allen, and Garnett.

In the 2007–08 season, Celtics completed the largest single-season turnaround in NBA history. The team went 66–16 in the regular season, a 42-game improvement over its 2006–07 record. However, the team struggled in the early rounds of the playoffs, needing seven games to defeat the Atlanta Hawks in the first round and another seven to defeat the Cleveland Cavaliers in the conference semifinals. The Celtics then beat the Detroit Pistons in six games in the Eastern Conference Finals, winning two road games.

For the 11th time in league history, and for the first time since 1987, the Celtics and the Lakers faced off in the NBA Finals. The Celtics won Game One at home 98–88, fueled by strong play by Garnett and Pierce's dramatic comeback from a second-half knee injury. They won Game Two 108–102 despite nearly blowing a 24-point lead in the fourth quarter. As the series shifted to Los Angeles, the Lakers stifled Pierce and Garnett in Game Three and won 87–81. However, the Celtics would overcome a 24-point deficit in Game 4 to win 97–91, making the largest in-game comeback in NBA Finals history. After again blowing a large lead, the Lakers hung on to win Game 5 103–98, sending the series back to Boston. In Game 6, the Celtics overpowered the Lakers, winning 131–92 and clinching their 17th NBA title. Paul Pierce was named Finals MVP. With the win the Celtics set a record for most games a team had ever played in a postseason with 26.

The 2008–09 Celtics started off the season at 27–2, the then-best starting record in NBA history. They also had a franchise-record 19-game streak. After the All-Star Break, Kevin Garnett was injured in a loss against the Utah Jazz and missed the last 25 games of the season. Garnett was eventually shelved for the playoffs. The 2009 Celtics still finished with 62 victories, but their playoff run would end against the Magic in the second round.

In 2009, with the return of Garnett from injury and the additions of Rasheed Wallace and Marquis Daniels, the Celtics started the season 23–5 and at one point had the best record in the NBA. However, Doc Rivers decided to lessen his aging stars' minutes to keep them fresh for the playoffs. As a result, the Celtics sputtered to an even 27–27 record the rest of the way and finished the 2009–10 regular season with a 50–32 record. Despite being the fourth seed in the Eastern Conference, the Celtics managed to make the NBA Finals. Rajon Rondo emerged as a star during postseason play. For the 12th time, the Celtics faced the Lakers in the Finals. After taking a 3–2 lead heading into Los Angeles for Game Six, the Celtics appeared poised to win their 18th title. However, starting center Kendrick Perkins suffered a severe knee injury early in Game Six, and the Celtics went on to lose the series in seven games.

During the 2010 off-season, with Perkins expected to be out until February 2011, the Celtics signed two former All-Star centers, Shaquille O'Neal and Jermaine O'Neal. Shaquille O'Neal's presence wound up leading to Perkins' departure: the Celtics were 33–10 in games Perkins had missed during the year due to injury and had a 19–3 record in games when O'Neal played over 20 minutes. Consequently, Perkins was traded to the Oklahoma City Thunder in February, when the Celtics were 41–14 and led the Eastern Conference despite another rash of injuries. Following the trade, however, they proceeded to win only 15 of their final 27 games. They finished with a 56–26 record, sliding to the third seed. The 2010–11 season still provided three landmarks: The Celtics became the second team to reach 3,000 victories, Paul Pierce became the third Celtic to score 20,000 points (the others are Larry Bird and John Havlicek), and Ray Allen broke the NBA record for most career three-pointers. The 2011 NBA playoffs started with the Celtics sweeping the New York Knicks 4–0 in the opening round. In the second round, they were ousted by eventual Eastern Conference champions Miami Heat in five games. Shaquille O'Neal, limited to 12 minutes in two games of the second round, retired at the end of the season.

The Celtics started the lockout-shortened season 0–3, as Pierce was out with a heel injury. At the All-Star break, the Celtics were below .500 with a 15–17 record. However, they were one of the hottest teams in the league after the break, going 24–10 the rest of the year and winning their fifth division title in a row. The Celtics made the playoffs as the fourth seed in the Eastern Conference. In the playoffs, the Celtics faced the Atlanta Hawks in the first round, beating them in six games led by strong play from Pierce and Garnett. In the conference semifinals, the Celtics defeated the 76ers in seven games. The Celtics faced the Miami Heat in the Eastern Conference Finals, losing in seven games to the eventual NBA champions.

The 2012 off-season started with the Celtics having only six players under contract. While Kevin Garnett was signed to a new contract, Ray Allen signed with the Miami Heat for less money than the Celtics offered; this move brought the five-year "Big Three" era to a somewhat acrimonious end. The Celtics finished the season with 41 wins. The Celtics trailed the New York Knicks 3–0 in the first round of the 2013 NBA playoffs before losing the series in six games. In Game Six, the Celtics nearly completed a comeback when they went on a 20–0 run to cut the lead to four.

During the off-season, head coach Doc Rivers was allowed to terminate his contract. He departed the Celtics to coach the Los Angeles Clippers, and the Celtics received a 2015 unprotected first-round pick as compensation. A few days later, Pierce, Garnett (who waived a no-trade clause), Jason Terry, and D. J. White, were traded to the Brooklyn Nets for Keith Bogans, MarShon Brooks, Kris Humphries, Kris Joseph, Gerald Wallace, and three future first-round draft picks (2014, 2016, 2018), together with the right to swap 2017 first-round picks with Brooklyn. The deal marked the start of a youth movement for the team.

On July 3, 2013, the Celtics announced that Brad Stevens, the head coach of Butler University, would replace Doc Rivers as head coach. Halfway through the season, in January, Rajon Rondo made his return and was named the 15th Team Captain in team history, and the team furthered the youth movement by acquiring two draft picks in a three-team trade that sent Jordan Crawford and MarShon Brooks to the Golden State Warriors while the Celtics received the Heat center Joel Anthony. The 2013–14 season marked the Celtics' first missed playoffs since the "Big Three".

The next off-season, the Celtics drafted Marcus Smart with the 6th overall pick and James Young with the 17th overall pick in the 2014 NBA draft, and signed Evan Turner. The 2014–15 season had several roster moves, the most prominent being Rondo and rookie Dwight Powell traded to the Dallas Mavericks for center Brandan Wright, forward Jae Crowder, veteran point guard Jameer Nelson, and future picks. A total of 22 players spent time with the Celtics, leading scorer and rebounder Sullinger suffered a season-ending left metatarsal stress fracture, and the team was only tenth in the East with 28 games remaining. However, midseason acquisition Isaiah Thomas helped the team win 22 of their last 34 games, finishing the season with a 40–42 record, enough for the seventh seed in the Eastern Conference Playoffs. The Celtics were swept by the second seeded Cleveland Cavaliers in the first round.

In the 2015 NBA draft Boston selected Terry Rozier, R.J. Hunter, Jordan Mickey, and Marcus Thornton with the 16th, 28th, 33rd, and 45th selections respectively. During the off-season, the Celtics signed forward Amir Johnson and traded Gerald Wallace and Chris Babb in exchange for Warriors forward David Lee. The Celtics finished the 2015–16 NBA season with a 48–34 record, earning the fifth seed in the Eastern Conference. They played the fourth seed Atlanta Hawks in the first round of the playoffs. After leading by 3 points in the fourth quarter of Game 1, guard Avery Bradley went down with a hamstring injury, making him sit out for the rest of the series. The Celtics lost the series 4–2 to the Hawks, ending their season.

In the 2016 NBA draft, the Celtics selected Jaylen Brown with the third pick. On July 8, 2016, the team signed four-time All-Star Al Horford. The Celtics finished the 2016–17 season with a 53–29 record and clinched the top seed in the Eastern Conference. After a hip injury ended Thomas' playoff run in game 2 of the Eastern Conference Finals, the Celtics eventually lost to the Cavaliers in five games. Isaiah Thomas was selected for his second straight All-Star game and first All-NBA selection, finishing third in the league in scoring and fifth in MVP voting. For the 2017 NBA draft, the Celtics won the draft lottery, earning them the first pick. They were projected to select freshman guard Markelle Fultz, but the pick was subsequently traded to the Philadelphia 76ers in exchange for the third pick in the 2017 draft and future picks. The 76ers would go on to draft Fultz, while the Celtics used the third pick to select freshman forward Jayson Tatum. During the off-season, the team signed Gordon Hayward. On August 22, 2017, the Celtics agreed to a deal that sent Isaiah Thomas, Jae Crowder, Ante Žižić, and the Brooklyn Nets' 2018 first-round draft pick to the Cleveland Cavaliers in exchange for Kyrie Irving.

By the end of the off-season, only four Celtics' players remained from the 2016–17 team, with Marcus Smart being the longest-tenured Celtic from the 2014 NBA draft. On the team's opening night game in the first quarter against the Cavaliers, Hayward suffered a fractured tibia and dislocated ankle in his left leg, causing him to be ruled out for the rest of the regular season. Despite the loss, the Celtics went on a 16-game winning streak, which also went down as the fourth-longest winning streak in the teams' history. The Celtics finished the year with a 55–27 record, good enough for second place in the Eastern Conference. In the playoffs, they defeated the Milwaukee Bucks in the first round in seven games, and continued the feat in the Conference Semifinals by defeating the Philadelphia 76ers in five games before losing to the Cleveland Cavaliers in seven games in the Conference Finals.

The Celtics finished the 2018–19 season with a 49–33 record. Analysts started questioning the team's performance and chances for the championship when the Celtics had a 10–10 record after the first 20 games on November 24, 2018. The Celtics then won the next eight games improving their record to 18–10. During the eight-game win streak, the Celtics defeated the Cleveland Cavaliers 128–95, the New York Knicks 128–100, and also defeated the Chicago Bulls by 56 points (133–77), setting a record for the largest margin in a victory in franchise history, while also tying the record for largest victory margin by an away team. The Celtics finished the regular season in fourth place in the Eastern Conference. During an April 7 game, Marcus Smart injured his hip and was ruled out for the rest of the regular season and the first round of the playoffs. In the 2019 playoffs, the Celtics swept the Indiana Pacers in the first round, and then lost to the Milwaukee Bucks in five games.

The Celtics held four picks in the 2019 NBA draft. Following a series of transactions, the team landed Romeo Langford with the 14th pick and also added Grant Williams, Carsen Edwards, and Tremont Waters (2020 G-league Rookie of the year). During the 2019 off-season, Irving and Horford signed with the Brooklyn Nets and Philadelphia 76ers, respectively. Irving left, despite promising to stay in Boston. On June 30, 2019, the Celtics and point guard Kemba Walker agreed to a four-year maximum contract worth $141 million. On July 6, 2019, the Celtics officially acquired Walker in a sign and trade with the Charlotte Hornets; the Celtics sent guard Terry Rozier and a protected 2020 second-round draft pick to Charlotte in exchange for Walker and a 2020 second-round draft pick. On July 1, 2019, the Celtics agreed to a two-year contract with center Enes Kanter.

Following the suspension of the 2019–20 NBA season, the Celtics were one of the 22 teams invited to the NBA Bubble to participate in the final 8 games of the regular season. In the 2020 playoffs, the Celtics swept the Philadelphia 76ers in the first round, beat the Toronto Raptors in a seven-game series, and fell to the Miami Heat in the Eastern Conference Finals in six games. Boston struggled with injuries in the 2020–21 season, with Walker, Tatum and Brown all missing games at different points in the season due to injury and COVID-19. Boston could not automatically qualify for the playoffs and were sent to the play-in tournament, where they defeated the Washington Wizards 119–100. In the playoffs, they lost to the Brooklyn Nets in five games.

On June 2, 2021, the Celtics named head coach Brad Stevens as president of basketball operations replacing Danny Ainge after he announced his retirement. On June 18, Stevens made his first transaction in his new position trading away Kemba Walker, the 16th pick in the 2021 NBA draft, and a 2025 second-round pick in exchange for former Celtic Horford, Moses Brown, and a 2023 second-round pick. On June 23, 2021, it was reported that Stevens had made the decision to hire Ime Udoka as his own replacement as head coach of the Celtics. Tatum made his third All-Star appearance off the bench at the 2022 NBA All-Star Game in Cleveland.

In April 2022, the Celtics qualified for the 2022 NBA playoffs as the second seed in the Eastern Conference, having a 51–31 record; they swept the Brooklyn Nets in the first round of the postseason. They next faced the Milwaukee Bucks in the Eastern Conference Semifinals and the Miami Heat in the Eastern Conference Finals, defeating both teams in seven-game series, earning the Celtics their first Finals appearance since 2010. The Celtics took a 2–1 series lead, but lost the next three games to lose to the Golden State Warriors 4–2.

In September, the Celtics suspended Udoka for the whole 2022–23 season for engaging in an improper intimate relationship with a female staffer. Assistant coach Joe Mazzulla replaced Udoka as the interim head coach. On February 16, 2023, Mazzulla was named the team's permanent head coach after leading the Celtics to a league-best 42–17 record at the NBA All-Star break. After overcoming a 3–2 deficit against the Philadelphia 76ers to advance to the Eastern Conference Finals, the Celtics fell behind 3–0 in a rematch against the Heat. They battled their way back to Game 7 thanks to a Derrick White buzzer-beater in Game 6, but the Heat ultimately prevented the first 3–0 comeback in NBA history with a decisive win in Boston.

During the 2023 off-season, the Celtics acquired Kristaps Porziņģis from the Wizards. In the trade, they sent Marcus Smart to the Memphis Grizzlies in a three-team deal, and also traded Grant Williams to the Dallas Mavericks. On October 1, 2023, the Celtics acquired Jrue Holiday in exchange for Malcolm Brogdon, Robert Williams III and two draft picks. On February 7, 2024, before the trade deadline, the Celtics acquired Xavier Tillman from the Grizzlies.

The Celtics finished the 2023–24 regular season with the best record in the NBA, securing a 64–18 record. After the regular season's close, the Celtics entered the 2024 NBA playoffs, defeating the Miami Heat in the first round, moving on to defeat the Cleveland Cavaliers in the East Semifinals, and moving on again to defeat the Indiana Pacers in the Eastern Conference Finals. The Celtics' victory in the Eastern Conference Finals on May 27, 2024, was accompanied by the announcement that Jaylen Brown had been selected as the NBA Eastern Conference Finals MVP, and Brown was presented with the Larry Bird trophy, the first of his career. The Celtics would go on to defeat the Dallas Mavericks in five games to win the NBA Finals, their record-setting 18th championship and breaking the tie with the Lakers (who have 17).