College basketball "madness" begins Tuesday with first-round elimination games in the NCAA men's basketball tournament -- a three-week ritual that fills social media, conversations, office betting pools and arenas in each region of the county. "March Madness is our annual endurance test to see how many hours of college basketball one nation can watch on TV," Greg Connors wrote Sunday in the Buffalo News. Every game is available, in high definition, on either CBS, TBS, TNT or truTV -- plus via online streaming, of course.

Thirty-one Division I teams gained automatic spots in the tournament by winning their conference titles this past weekend or earlier. Harvard, which got in that way this time, is making its first appearance in 66 years. (See video below.) A NCAA committee Sunday night announced at-large selections for 37 more teams. Excitement is generated partly by rooting for local or home state teams, or schools attended by friends or family members. Interest also flows from the live-action drama of underdog triumphs and long-shot victories at the final buzzer. With 33 games, a David-beats-Goliath surprise happens most years.

The madness, as it's called, culminates with Final Four semifinal and final games that begin March 31 at the Mercedes-Benz Superdome in New Orleans, home of the NFL's Saints. The NCAA women's tournament, with selections announced Monday, runs through an April 1-3 championship series in Denver. Off the court, the tournament is a big business, generating more than 95 percent of yearly revenue for the National Collegiate Athletic Association from broadcast rights, a share of ticket fees, sponsorships and merchandise sales.

Blogger says: "An amazing aspect of the tournament is the upsets that catch everyone off-guard and shock the sport. Nothing feels quite like watching a No. 1 seed lose in the first round." -- Donald Wood, BleacherReport.com columnist

Player says: "People I didn’t know were stopping to congratulate me. My teachers were sending me emails asking about the NCAA tournament." -- Oliver McNally, Harvard senior and team co-captain

What are brackets? The NCAA pairs teams against each other in the tournament’s opening rounds based on their records this season and other factors. Those pairings, displayed on a chart printed and posted by newspapers, are known as brackets. This year's were revealed Sunday night.