A1 (stylised as a1) is a British–Norwegian boy group formed in 1998. The original lineup consisted of Paul Marazzi, Christian Ingebrigtsen, Mark Read and Ben Adams. Ingebrigtsen is originally from Oslo, Norway, while the other members originate from London.

Their debut single, "Be the First to Believe", entered the UK singles chart at number six in mid-1999. They achieved chart success in the UK and other parts of the world in the late 1990s and early 2000s, particularly Southeast Asia. In the UK, they scored two number ones and six other top 10 hits, seven of which were written by the band. Adding to this, they also won a Brit Award for "British Breakthrough Act" in 2001. They were managed by band manager Tim Byrne, who also formed Steps.

Marazzi left the band in 2002, citing personal reasons. The three remaining members subsequently decided to split due to exhaustion from being on the road for the best part of four years straight.

In December 2009, Ingebrigtsen, Read and Adams reformed a1, without Marazzi, in Norway for a series of concerts at the Christiania Theatre in Oslo. Since their comeback, they have released new singles as well as their fourth and fifth studio albums, Waiting for Daylight, in 2010, and Rediscovered, in 2012.

In 2014, A1 appeared on the ITV2 documentary The Big Reunion along with other bands such as Eternal, Damage, Girl Thing, 3T and a new band called 5th Story, made up of Dane Bowers (from Another Level), Gareth Gates, Kenzie (from Blazin' Squad), Kavana and Adam Rickitt.

In 2017, Marazzi met his former bandmates in Newcastle after his 15-year absence, and he will appear on their 20th anniversary tour.