The 2021 NCAA Division I men's basketball tournament was a single-elimination tournament of 68 teams to determine the National Collegiate Athletic Association (NCAA) Division I men's college basketball national champion for the 2020–21 season. The 82nd edition of the tournament began play on March 18, 2021 in sites around the state of Indiana,^[2] and concluded with the championship game at Lucas Oil Stadium in Indianapolis on April 5, with the Baylor Bears defeating the previously undefeated Gonzaga Bulldogs 86–70 to earn the team's first ever title.

For logistical considerations surrounding the ongoing COVID-19 pandemic (which resulted in the cancellation of the previous year's tournament), the NCAA announced in January 2021 that all tournament games would be held in Indiana rather than at sites across the country. This was the only time in the history of the tournament to date that a single state has hosted it in its entirety.^[3]

This marked the first time since 1976 that neither Duke nor Kentucky qualified for the tournament.^[4] It was also the first time since 1995 that Duke failed to make the tournament, breaking a streak of 24 consecutive appearances. America East champion Hartford and WAC champion Grand Canyon made their NCAA Tournament debuts.

The tournament was marked by many upsets, with Yahoo Sports journalist Pete Thamel calling it "one of the most dizzying NCAA men's tournaments in history". With only half of the 16 second-round games having been played, there had been 11 upsets to that point, using the NCAA's definition of "upset" as a win by a team seeded five or more lines below its defeated opponent. This had already broken the record for most upsets prior to the round of 16; by the end of the second round, this number went up to 12. In addition, at least one team seeded #9 through #15 won a first-round game for the fourth time ever, and the first time since 2016. Also, a record four teams seeded 13 or lower won first-round games.^[5] Another notable mark set during the tournament was a record-breaking 14 upsets throughout the event, breaking the original record of 13 upsets from the 1985 and 2014 tournaments.

The Final Four game between UCLA and Gonzaga (the first semifinal game to go into overtime since 1998) saw a game-winning buzzer-beater by Jalen Suggs to take Gonzaga into the championship game, the first buzzer-beater in a national semifinal since 1977. By defeating Gonzaga in the championship game, the Baylor Bears became the second consecutive first-time NCAA champions, following the Virginia Cavaliers in 2019. The last time this happened was in 2002 and 2003, when the Maryland Terrapins and Syracuse Orange (then nicknamed Orangemen) won their first titles in their respective years. Baylor also joined Texas Western (now known as the University of Texas at El Paso) as the only two teams from the state of Texas to have won an NCAA Division I Basketball championship, the Miners having done so in 1966.

A total of 68 teams entered the 2021 tournament, with 31 of them (down from 32, due to the Ivy League having canceled all winter semester sports due to COVID-19)^[6] having received an automatic bid by winning their conference's tournament. The remaining 37 bids were "at-large", with selections extended by the NCAA Selection Committee. Teams met sport sponsorship requirements and were considered for NCAA championship selection if they played 13 games, which represented a 50 percent reduction of the current minimum. For NCAA championship consideration, all 13 games had to be against other Division I opponents. Teams could also play 12 regular-season games against Division I opponents and one conference tournament game to be eligible for tournament consideration.^[7]

The Selection Committee seeded the entire field from 1 to 68. The four lowest-seeded automatic qualifiers and the four lowest-seeded at-large teams played in the First Four round: for the 2021 tournament, the games were played between the overall 65th and 66th seeds, the 67th and 68th seed, and the last four at-large seeds.^[8]

The top four teams outside of the ranking (commonly known as the "first four out" in pre-tourney analyses) acted as standbys in the event a school was forced to withdraw from the tournament due to COVID-19 protocols.^[9][10] However, if a team withdrew within 48 hours of the tournament's commencement, they would not be replaced; the bracket was not reseeded, and the affected team's opponent would automatically advance to the next round.The replacement teams are as follows, in order:

^[12]

On January 4, 2021, the NCAA announced that due to logistical considerations associated with the COVID-19 pandemic (which prompted the cancellation of the 2020 tournament), the entirety of the tournament would be conducted at sites within the Indianapolis metro area and central Indiana, rather than across the country.^[13] Players stayed at hotels near the Indiana Convention Center, which served as the main practice facility.^[14] Lucas Oil Stadium had two courts named "Unity Court" and "Equality Court" during the First Round, Second Round, and Elite Eight.

On February 19, it was announced that all venues would operate at a maximum of 25% capacity. As this capacity includes staff and players, the exact number of spectators varied by venue.^[15][16] Artificial crowd noise was used at all venues to augment the limited in-person attendance.^[17]

This tournament marked the first time ever that Indiana Farmers Coliseum was a tournament venue, the first time since 2017 that Bankers Life Fieldhouse was a tournament venue, the first time since 1940 that Hinkle Fieldhouse was a tournament venue, the first time since 1980 that Mackey Arena was a tournament venue, and the first time since 1981 that Assembly Hall was a tournament venue.

First Four:

• Thursday, March 18
  • Mackey Arena, West Lafayette, Indiana (Host: Purdue University)
  • Simon Skjodt Assembly Hall, Bloomington, Indiana (Host: Indiana University Bloomington)

First and Second Rounds:

• Friday, March 19 and Saturday, March 20
  • Mackey Arena, West Lafayette, Indiana (Host: Purdue University)
  • Simon Skjodt Assembly Hall, Bloomington, Indiana (Host: Indiana University Bloomington)
  • Bankers Life Fieldhouse, Indianapolis, Indiana (Host: Ball State University)
  • Hinkle Fieldhouse, Indianapolis, Indiana (Host: Butler University)
  • Indiana Farmers Coliseum, Indianapolis, Indiana (Host: IUPUI)
  • Lucas Oil Stadium, Indianapolis, Indiana (Unity Court and Equality Court) (Hosts: IUPUI, Horizon League)
• Sunday, March 21 and Monday, March 22
  • Bankers Life Fieldhouse, Indianapolis, Indiana (Host: Ball State University)
  • Hinkle Fieldhouse, Indianapolis, Indiana (Host: Butler University)
  • Indiana Farmers Coliseum, Indianapolis, Indiana (Host: IUPUI)
  • Lucas Oil Stadium, Indianapolis, Indiana (Unity Court and Equality Court) (Hosts: IUPUI, Horizon League)

Regional Semifinals and Finals (Sweet Sixteen and Elite Eight):

• Saturday, March 27 and Sunday, March 28
  • Bankers Life Fieldhouse, Indianapolis, Indiana (Host: Ball State University)
  • Hinkle Fieldhouse, Indianapolis, Indiana (Host: Butler University)
• Monday, March 29 and Tuesday, March 30
  • Lucas Oil Stadium, Indianapolis, Indiana (Unity Court and Equality Court) (Hosts: IUPUI, Horizon League)

National Semifinals and Championship (Final Four and Championship):

• Saturday, April 3 and Monday, April 5
  • Lucas Oil Stadium, Indianapolis, Indiana (Hosts: IUPUI, Horizon League)

Note: Unlike past tournaments, teams are not grouped as pods. Second round games will match teams that played at different venues in the first round.

^† Includes a game declared no-contest due to COVID-19 protocols with VCU. Oregon of the Pac-12 conference advanced to the second round and VCU of the Atlantic 10 conference was eliminated from the tournament.

• The FF, R64, R32, S16, E8, F4, CG, and NC columns indicate how many teams from each conference were in the First Four, Round of 64 (first round), Round of 32 (second round), Regional semifinals (Sweet 16), Regional Finals (Elite Eight), National semifinals (Final Four), National Championship Game, and national champion, respectively.
• The Record column does not include wins or losses in games declared no-contest.

• 2021 NCAA Division I women's basketball tournament