It is the fourth track on their debut album, All Killer No Filler (2001), and was released as the lead single in April 2001.

It is the band's most successful single to date, topping the Billboard Modern Rock Tracks chart.

"Fat Lip" was written by Sum 41 members Deryck Whibley, Steve Jocz and Dave Brownsound, and in-house producer Greig Nori, with production by Jerry Finn.

The song gets its title from the slang term for a swollen lip as a result of being punched in the face.

I changed a few things and made it work, now all of a sudden I was like, 'OK, I've got the rap part, I've got a riff, and I've got a chorus.'

The song was performed on Saturday Night Live on October 6, 2001, hosted by Seann William Scott.