The 2006 NCAA Division I men's basketball tournament involved 65 teams playing in a single-elimination tournament to determine the national champion of men's NCAA Division I college basketball as a culmination of the 2005–06 basketball season. It began on March 14, 2006, and concluded with the championship game on April 3 at the RCA Dome in Indianapolis, Indiana.

The Final Four featured no top seeds for the first time since the tournament expanded to 64 teams in 1985 (the first time since 1980), with the highest remaining seed being Oakland region winner, #2 UCLA, making their first Final Four appearance since their 1995 national championship. For only the second time in history, an 11-seed advanced to the Final Four as George Mason of the Colonial Athletic Association (CAA) won the Washington, D.C. region. Those two teams were joined by Atlanta region winner LSU (who was the first team to advance to the Final Four as an 11-seed in 1986), and Minneapolis region winner Florida, who had not made the Final Four since their runner-up finish in 2000 also in Indianapolis.

Florida won its first-ever national basketball championship by defeating UCLA 73–57 in the final game. Florida's Joakim Noah was named the Most Outstanding Player of the NCAA tournament.

George Mason's run was one of several upsets by lower-seeded teams in the tournament. For the second consecutive year, a No. 14 seed beat a No. 3 seed as Northwestern State defeated Iowa. No. 13 seed Bradley also defeated No. 4 seed Kansas and advanced to the Sweet Sixteen by defeating No. 5-seeded Pittsburgh in the second round. Two No. 12 seeds won as well, as Montana and Texas A&M both won their respective First round matchups. For the second straight year, Milwaukee won as a double-digit seed, this time as the No. 11-seeded Panthers defeated Oklahoma in the first round.

American East Conference champion Albany and ASUN champion Belmont made their first appearance in the tournament.

A total of 65 teams were selected to participate in the tournament. Of that total, 31 of the teams earned automatic bids by winning their conference tournaments. Penn earned an automatic bid by winning the regular-season title of the Ivy League, which did not conduct a conference tournament. The remaining 34 teams were granted "at-large" bids, which are extended by the NCAA Selection Committee.

The initial game on March 14 officially named the opening round game, but popularly called the "play-in game", had Monmouth, winner of the Northeast Conference tournament, facing Hampton, who won the Mid-Eastern Athletic Conference tournament, for a chance to play top seed Villanova in the first round of the Tournament. Monmouth defeated Hampton, 71–49, to advance to play Villanova.

All teams were seeded from 1 to 16 within their regions. The Selection Committee seeded the entire field from 1 to 65. In a practice used since 2004, the ranking of the four top seeds against each other would determine the pairings in the Final Four. The top overall seed would be seeded to play the fourth overall seed in the national semifinals, should both teams advance that far. In 2006, these rankings were as follows: No. 1 Duke, No. 2 Connecticut, No. 3 Villanova, and No. 4 Memphis.^[1]

San Diego

Salt Lake City

Dallas

Auburn Hills

Dayton

Jacksonville

Greensboro

Philadelphia

2006 play-in game (orange) and first and second rounds (green)

Oakland

Minneapolis

Atlanta

Washington, D.C.

Indianapolis

2006 Regionals (blue) and Final Four (red)

The following are the sites that were selected to host each round of the 2006 tournament:

Opening Round

• March 14
  • University of Dayton Arena, Dayton, Ohio (Host: University of Dayton)

First and Second Rounds

• March 16 and 18
  • Cox Arena, San Diego, California (Host: San Diego State University)
  • Greensboro Coliseum, Greensboro, North Carolina (Host: Atlantic Coast Conference)
  • Jacksonville Veterans Memorial Arena, Jacksonville, Florida (Host: Jacksonville University)
  • Jon M. Huntsman Center, Salt Lake City, Utah (Host: University of Utah)
• March 17 and 19
  • American Airlines Center, Dallas, Texas (Host: Big 12 Conference)
  • The Palace of Auburn Hills, Auburn Hills, Michigan (Hosts: Oakland University, Mid-Continent Conference)
  • University of Dayton Arena, Dayton, Ohio (Host: University of Dayton)
  • Wachovia Center, Philadelphia, Pennsylvania (Host: Atlantic 10 Conference)

Regional semifinals and finals (Sweet Sixteen and Elite Eight)

• March 23 and 25
  • Atlanta Regional, Georgia Dome, Atlanta, Georgia (Host: Georgia Tech)
  • Oakland Regional, Oakland Arena, Oakland, California (Hosts: University of San Francisco, West Coast Conference)
• March 24 and 26
  • Minneapolis Regional, Hubert H. Humphrey Metrodome, Minneapolis, Minnesota (Host: University of Minnesota)
  • Washington, D.C. Regional, Verizon Center, Washington, D.C. (Host: Georgetown University)

National semifinals and championship (Final Four and championship)

• April 1 and 3
  • RCA Dome, Indianapolis, Indiana (Hosts: Butler University, Horizon League)

*Monmouth University won the Opening Round game.

The America East, Atlantic Sun, Big South, Big West, Ivy, MAAC, MAC, MEAC, Ohio Valley, SoCon, SWAC, Mid-Continent, and Sun Belt conferences all went 0–1.

The columns R32, S16, E8, F4, and CG respectively stand for the Round of 32, Sweet Sixteen, Elite Eight, Final Four, and championship Game.

• Jim Nantz and Billy Packer – First & Second Round at Philadelphia, Pennsylvania; Minneapolis Regional at the Hubert H. Humphrey Metrodome; Final Four at Indianapolis, Indiana
• Dick Enberg and Jay Bilas – First & Second Round at San Diego, California; Atlanta Regional at the Georgia Dome
• Verne Lundquist/Bill Raftery/Mike Gminski – First & Second Round at Auburn Hills, Michigan; Washington, D.C. Regional at the Verizon Center
• Gus Johnson and Len Elmore – First & Second Round at Dayton, Ohio; Oakland Regional at the Oakland Arena
• Kevin Harlan and Dan Bonner – First & Second Round at Greensboro, North Carolina
• Ian Eagle and Jim Spanarkel – First & Second Round at Salt Lake City, Utah
• Craig Bolerjack and Bob Wenzel – First & Second Round at Dallas, Texas
• Tim Brando, Stephen Bardo, and Mike Gminski – First & Second Round at Jacksonville, Florida

Greg Gumbel once again served as the studio host, joined by analysts Clark Kellogg and Seth Davis.

• 2006 NCAA Division II men's basketball tournament
• 2006 NCAA Division III men's basketball tournament
• 2006 NCAA Division I women's basketball tournament
• 2006 NCAA Division II women's basketball tournament
• 2006 NCAA Division III women's basketball tournament
• 2006 National Invitation Tournament
• 2006 Women's National Invitation Tournament
• 2006 NAIA Division I men's basketball tournament
• 2006 NAIA Division II men's basketball tournament
• 2006 NAIA Division I women's basketball tournament
• 2006 NAIA Division II women's basketball tournament

• The futures of two of this year's Final Four teams would be polar opposites of the other two in 2007. Both George Mason and LSU would fail to receive a bid to either the NCAA tournament or the NIT, while both Florida and UCLA would return to the Final Four (the two teams would have a rematch, this time in the semifinals, with the same result, a Florida victory).
• George Mason became the first team from a "mid-major" conference to reach the Final Four since UNLV's loss to Duke in 1991.
• This was the second of four Final Fours to feature no No. 1 seeds (1980, 2011, and 2023 being the others).
• Duke was the last team before Florida to win back-to-back titles, and like Florida, they won their first of the two in Indianapolis at the RCA Dome.