The Sing-Off is an American television singing competition featuring a cappella groups. It debuted on NBC on December 14, 2009, and is produced by Sony Pictures Television and Outlaw Productions, with Mark Burnett's One Three Media being added for the fourth season.
It is hosted by Nick Lachey, with judges Ben Folds, Shawn Stockman, and originally Nicole Scherzinger, later replaced by Sara Bareilles. Bareilles left the show after one season and was replaced by Jewel. The show's music staff all came from the a cappella community: Deke Sharon, Bill Hare, Ed Boyer, Ben Bram, Robert Dietz, Christopher Diaz and Nick Girard.
A cappella groups from the United States, including Puerto Rico, were chosen by audition and advanced in the competition based on judges' eliminations until the finale, with the winners being determined by viewer votes.
The program has featured guest appearances by various popular artists, including Bobby McFerrin, Natasha Bedingfield, Jay Sean, Smokey Robinson, Neil Diamond, Boyz II Men, and Sara Bareilles.
The Sing-Off was renewed for a third season and started airing much earlier on September 19, 2011, although the first two series had been broadcast in December. Unlike previous seasons, the early start in September allowed for the production of more episodes and the number of participant groups increased.