+44 (read as Plus 44) was an American alternative rock band formed in Los Angeles, California in 2005. The group consisted of vocalist and bassist Mark Hoppus and drummer Travis Barker of Blink-182, lead guitarist Shane Gallagher of The Nervous Return and rhythm guitarist Craig Fairbaugh of Mercy Killers. Hoppus and Barker created +44 shortly after the 2005 breakup of Blink-182, and the band's name refers to the international dialing code of the United Kingdom, the country where the duo first discussed the project. Early recordings were largely electronic in nature, and featured vocals by Carol Heller, formerly of the all-girl punk quartet Get the Girl.

The band's sound gradually took on a heavier tone as Hoppus and Barker purchased a studio in which to record. Although hotly anticipated by music press, the band's debut, When Your Heart Stops Beating (2006), undersold commercial expectations and received mixed reviews from professional critics. The group toured worldwide throughout 2006 and 2007, including a summer slot on the Honda Civic Tour alongside Fall Out Boy. Hoppus later began preparing material for a solo album and put plans for a second +44 album on hold in 2008, and the group entered an extended hiatus with the reunion of Blink-182 in 2009. On the subject of the band's future, Hoppus has commented, "I don't consider it done. We'll never say never with anything."