"Missing" is a B-side for the first studio album, Fallen. Its initial release was included on the Australian version of the "Bring Me to Life" single CD. In 2004, it was released again as a bonus track on Anywhere but Home, followed by another release in late 2016 on Lost Whispers.
The song was initially recorded as a demo in the pre-production of the band's debut album, Fallen. It was then finally recorded, but didn't make the cut on the album.
In a 2012 interview, Amy was asked about the meaning of the song:
One fan actually went so far as to say that after her mother passed away she would listen to the song “Missing”, she was wondering about the meaning behind the song and if she is understanding it right being the missing of someone lost?
As far as if she got it right, I would say you always get it right. When it comes to music and art it’s always about how each individual interprets it. Some of our songs are self reflective but some of them are also story telling. For me that song was all about running away, but its poetry so please do take from it what you can.
The background vocals also appear in the end of the live version of Exodus that was performed on May 7, 1999.