G4 are a four-piece British vocal troupe who first came to prominence when they finished second in Series 1 of The X Factor in 2004, and are known for their operatic delivery of modern pop songs. Originally a barbershop quartet, the members met at the Guildhall School of Music and Drama, from which the name G4, standing for "Guildhall 4", derives.

In 2007 the band disbanded, citing disagreements among the members, but reunited in 2014 to celebrate their ten-year anniversary with a number of concerts nationwide, leading to a new album for Christmas 2015.

The group currently consists of original members tenor Jonathan Ansell and baritone Mike Christie, with Jai McDowall joining after Lewis Raines left in 2023, while Duncan Sandilands replaced former bass singer Nick Ashby in 2019, who had replaced original bass Matt Stiff in 2014.