Fans and players alike are preparing for the beginning of the NCAA (National Collegiate Athletic Association) Men's Division One basketball tournament.  Sixty-five colleges and universities from across the country fight for survival, either ending their season or winning the national championship. The games have taken on an even larger significance in recent years as millions of fans place bets based on their predictions of whom will win all 64 games.

It is called "March Madness."  The climax of the college basketball season comes over three weeks in late March, when 65 schools and universities battle to become the national champion.

College fans pack bars to cheer on their teams during what has become one of the most popular U.S. sporting events.

The most competitive school teams in the NCAA play.  Lose, and a team's season is over.

And around America, in offices and at home, thousands wager on the outcome of each game.  Fanatics and casual viewers, alike, fill out tournament brackets before the games start.  

"I just literally go from the top, and I say o.k., Kansas vs. Prairie View A&M.  I've never heard of Prairie View A&M, so Kansas it is," one fan said.

The game for betters is predicting which teams advance into the later rounds, known as the "Sweet Sixteen," the "Elite Eight" and the "Final Four" and the champion.

The chances of predicting all 64 games correctly? A website dedicated to sports gambling calculates that at one in over 9.2 quintillion. That is the number 9 followed by 18 zeroes.

The estimates on how much money people wager run into the billions of dollars, putting "March Madness" behind only the Super Bowl.

The tournament's allure is the fact that underdogs, or "Cinderella" teams (not favored to win) often upset nationally-known powerhouse teams.  In 2006, George Mason University, a little known Virginia school, made a stunning run to the Final Four.  And last year, tiny Davidson College from the southern state of North Carolina nearly made it as far.

Virginia governor Tim Kaine favors his state's underdog, Virginia Commonwealth University.

"I think VCU matches up against UCLA [University of California, Los Angeles] very well. So, it'll be a lot of fun, I know all Virginians will be writing their brackets favoring the home team. I know, I'm going to - I'm gonna favor the home teams in the brackets that I write," he said.

Even national leaders get into the game.  Then-Senator Barack Obama played some pick-up hoops with the University of North Carolina stars as he was running for president last year.

And in an interview with the sports TV network ESPN, President Obama picked the university's team to win it all this year.

"Is there a drumroll? I'm going with the Tar Heels. The Tar Heels that are watching, I picked you last year, and you let me down. This year, don't embarass me in front of the nation," the president said.

But any of the 64 teams, theoretically, could string together six wins straight starting this weekend and win the crown.  And to the fanatics, that is what puts the "madness" in March Madness.