Sixty-eight (68) teams line up with a chance to win the national title. It's not just the best 68 teams from among the more than 350 teams that play Division I basketball, though. Teams are split into 32 conferences, and each of those conferences has an automatic bid. Every conference plays a season-ending conference tournament, and gives the automatic bid to the winner. The other 36 teams are chosen by a selection committee. They are called at-large bids, and they generally go to the 36 most deserving teams. Obviously it is a very difficult job to pick the 36 best teams, and the process is very subjective and can be very controversial.
The four lowest ranked automatic bid teams and the four lowest ranked at-large teams in the tournament play in special play-in games called the First Four before the tournament. The rest of the field is split into four regions of 16 teams, and those regions are seeded from one to 16. The top team in each region plays the 16th team, the second plays the 15th and so on. The winners of each game goes on to the next round and so on until only one team is standing. A team is knocked out of the tournament and has to go home as soon as they lose once, so the pressure is incredibly intense.
The tournament takes place over three weekends starting soon after the middle of March.
Perhaps the biggest key to the tremendous popularity of the tournament is the bracket. The March Madness bracket is the grid of all the teams in the tournament and the path they have to follow to the Final Four and the championship game. Filling out a bracket with the winners of each of the 67 games in the tournament is an incredibly difficult task, and nobody has successfully filled out a perfect bracket. Odds of a perfect bracket are estimated to be 1 in 9,223,372,036,854,775,808 (9.2 quintillion). Some March Madness contests are free to enter, others require an entry fee. Many businesses utilize pool hosting services to run their pools, allowing them the flexibility to customize the pool rules and display.
March Madness has become one of the most popular sporting events in the United States. Because of the length of the tournament and the number of teams involved it is one of the most popular sporting events in terms of television ratings. One event associated with March Madness is filling out the brackets. It has become extremely common in popular culture, even among non-sports fans; it is estimated that tens of millions of Americans participate in the contest every year. Mainstream media outlets such as ESPN, CBS Sports and Fox Sports host tournaments online where contestants can enter for free. Employers have also noticed a change in the behavior of employees during this time: they have seen an increase in the number of sick days used, extended lunch breaks and even the rescheduling of conference calls to allow for more tournament watching. There are also many handicappers and pundits which offer advice for winning your bracket.