“What Hurts the Most” is a country music song written by Jeffrey Steele and Steve Robson. It was originally recorded by American country music singer Mark Wills on his 2003 album And the Crowd Goes Wild. It was to be released as a single, but he was dropped from his label before the song could be released. (Nonetheless, Wills’s version reached #51 on the Hot Digital Songs chart in 2006.)
The song also appeared on Jeffrey Steele’s album You Gotta Start Somewhere in the same year. In 2004, Bellefire, a pop group, recorded the song for an album, but did not release it as a single either.

In 2006, country music trio Rascal Flatts released the song as a single for their album Me and My Gang, and it became their fifth number-one single on Billboard’s Hot Country Songs chart. It also peaked at No. 6 on the all-genre Billboard Hot 100, becoming the band’s first Top 10 pop hit. In addition, the song reached #1 on the Adult Contemporary charts. Rascal Flatts also performed the song live with Kelly Clarkson at the Academy of Country Music Awards in 2006.

Rascal Flatts’ recording earned two nominations for the 49th Annual Grammy Awards, in the categories of Best Country Performance by a Duo or Group with Vocals, and Best Country Song.