"Mercy" is a song performed by Welsh singer Duffy, released as the second single from her debut studio album, Rockferry (2008). Co-written by Duffy and Steve Booker and produced by Booker, it was released worldwide in 2008 to critical acclaim and unprecedented chart success. As Duffy's first international release, the song is credited with firmly establishing her career and is now considered her signature song. "Mercy" received comparisons to Duffy's previous single, "Rockferry". Critical reviewers of "Mercy" noted similarities between the song to releases by Aretha Franklin, Dusty Springfield and the Supremes, as well as contemporaries such as singer Amy Winehouse.