The Biggest Loser is an American competition reality show that debuted on NBC on October 19, 2004. The show features obese or overweight contestants competing to win a cash prize by losing the highest percentage of weight relative to their initial weight.

Update: I have seen all, but last season of The Biggest Loser. Wow! And I don't complain about overweight, it's just a very great TV show, featuring trainers like Bob Harper,  Jillian Michaels, Dolvett Quince and others. 

Each season of The Biggest Loser starts with a weigh-in to determine the contestants' starting weights, which serve as the baseline for determining the overall winner.

The contestants are grouped into teams of three, each wearing separate colored T-shirts. Depending on the season a team may work with a specific trainer or all trainers may work with all contestants. The trainers are responsible (in conjunction with medical personnel retained by the show) for designing comprehensive workout and nutrition plans and teaching them to the contestants. However, the contestants are individually responsible for implementing the principles taught.

During an episode, various challenges and temptations (see below) are featured. Those who win a particular challenge are given special privileges, such as a weight advantage for the next weigh-in or even full immunity from being voted off the show.