The 68 teams that make up the NCAA Tournament field are selected by the NCAA Selection Committee, made up of Athletic Directors and Conference Commissioners. The committee will have spent the prior week locked in a room, putting together the bracket. Shortly after the field is finalized, the NCAA Tournament bracket is announced on CBS, with the likes of Greg Gumbel, Greg Anthony, and Seth Davis in the studio. And immediately after that, you can find printable brackets and Tournament predictions here on Collegehoops.net.
For many college basketball fans, Selection Sunday evening is the best day of the college basketball season.. even surpassing the National Championship game. There is inevitably controversy over which "bubble" teams did or did not make the field, as well how the teams were seeded. Once the controversy dies down, the games begin shortly after on Tuesday, March 13th, as the "First Four" games take place before the Tournament-proper starts on Thursday.
The field consists of the following:
Automatic bids - These bids, 31 in all, go to conference champions. Of these bids, 30 go to conference tournament champions. Most conferences have their tournaments on the week preceding Selection Sunday. The Ivy League is the only conference that does not conduct a postseason tournament; in that conference, the regular-season champion receives the automatic bid.
At-large bids - These are schools that the NCAA selection committee deems worthy of a tournament bid. The NCAA tournament has 37 at-large bids available. The selection committee takes great care to treat teams fairly based on their overall resume, as opposed to being biased by team prestige and conference prestige. To this end, the committee uses various computer rankings, most notably the RPI. However, history has shown that the highest ranked RPI team not to make the tournament is almsot inevitably from a "mid-major" conference.
Here's the NCAA Selection Committee principles for putting together the bracket..
Check out Shawn Siegel's Bracketology for projections of who will be selected.
For more Selection Sunday information.. see the ole Wiki.