The NCAA Men's Division I Basketball Championship is a single elimination tournament held each spring featuring 65 college basketball teams in the United States. Colloquially known as March Madness (as the tournament takes place mainly during the month of March) or the Big Dance (as opposed to the now smaller and less prestigious NIT), the tournament takes place over 3 weeks at sites across the United States, and the national semifinals (the Final Four) have become one of the nation's most prominent sporting events.
Since its 1939 inception (a brainchild of Phog Allen at the University of Kansas), it has built a legacy that includes dynasty teams and dramatic underdog stories. In recent years, friendly wagering on the event has become something of a national pastime, spawning countless "office pools" that attract expert fans and novices alike. All games of the tournament are broadcast on the CBS broadcast television network in the United States, except for the Opening Round game (or "play-in game" as it has been called), which aired on TNN in 2001, and ESPN since 2002.
The tournament bracket is made up of conference tournament champions from each Division I conference, which receive automatic bids. The remaining slots are at-large berths, with teams chosen by an NCAA selection committee. The selection process and tournament seedings are based on several factors, including team rankings, win-loss records and RPI data.
Two low-seeded teams (typically teams with poor records that qualified by winning their conference tournament championships) play the "opening round" game to determine which will advance into the first round of the tournament, with the winner advancing to play the top seed in one of the four regions. The opening Round game was added in 2001 and has been played in University of Dayton Arena in Dayton, Ohio each subsequent year. The opening round is considered part of the tournament and is often referred to as a "play-in" game.
A total of 65 teams qualify for the tournament played in March and April. Thirty-one of the teams earn automatic bids by winning their respective conference tournaments. Because the Ivy League does not conduct a post-season tournament, its regular-season conference champion receives an automatic bid. The remaining teams are granted at-large bids, which are extended by the NCAA Selection Committee.
The tournament is split into four regions and each region has teams seeded 1–16, with the committee making every region as comparable to the others as possible. The best team in each region plays the #16 team, the #2 team plays the #15, and so on. The effect of this seeding structure ensures that the better a team is seeded, the worse-seeded their opponents will be.
Two teams play a play-in game game on the Tuesday preceding the first weekend of the tournament, with the winner of that game advancing to the main draw of the tournament and plays a top seed in one of the regionals. This game has been played at the University of Dayton Arena in Dayton, Ohio since its inception in 2001. This game originated in 2001 with the addition of the Mountain West Conference (and its automatic bid into the tournament) after the NCAA tournament committee opted to include an additional team and play in game in lieu of taking away one of the 34 "at-large" bids. These two teams share equally in the share of funds as if they had qualified for a first round game, and wins in the opening round game are considered wins in the NCAA tournament. Thus, properly, the tournament has 65 teams, although in practice most brackets only include the 63 teams, with one spot blank (to be filled in after the play-in game). Since no #16 seed has ever beaten a #1 seed in the men's championship, the result of the opening round game is largely deemed irrelevant for bracket-filling purposes.
