Fun (often written as fun.) is an American indie pop band based in New York, New York that was formed by Nate Ruess, formerly of The Format. Ruess left Arizona to develop his career in New York City. Ruess formed the band with Andrew Dost of Anathallo and Jack Antonoff of Steel Train. Fun recorded their debut album, Aim and Ignite in August 2008 with producer Steven McDonald and arranger Roger Joseph Manning Jr., the former keyboardist of Jellyfish.

Fun made its first single, "At Least I'm Not As Sad (As I Used To Be)" available as a free download by signing up for the band's mailing list." In addition, the band announced that if Fun's Facebook page reached 40,000 fans by December 1st, a new Christmas single, "Believe In Me," would be released for free download. This goal was met, and Fun did indeed release the single for free.

In February of 2010, Fun supported Jack's Mannequin on their headline tour, along with Vedera which was followed by their first UK appearances in March. Their current touring band also includes Rob Kroehler, Emily Moore, Nate Harold, and Jon "Jonny Thunder" Goldstein.

In April of 2010, Fun supported Paramore's headline tour. Other support for the tour includes Relient K.The band then embarked on a full UK tour in May.