"Mercy" is a soul song by the Welsh singer Duffy, written by Duffy and Steve Booker, who co-wrote and produced it; Duffy had written the lyrics before meeting him. It is the second single from her debut album Rockferry (2008), released on 11 February 2008 on A&M, with the B-sides "Save It for Your Prayers" and "Tomorrow". It was written in about two weeks at the end of the album sessions.
The song is in common time at 130 bpm, in G Dorian, and follows a 12-bar blues form on I7, IV7 and V7. Its intro resembles "Stand by Me" by Ben E. King, with a flattened seventh. Critics compared Duffy to Aretha Franklin, Dusty Springfield and Amy Winehouse, and Digital Spy called it a Northern soul pastiche. It topped the UK Singles Chart for five weeks from February 2008 and reached number one in Austria, Germany, Greece, the Netherlands, Norway, Ireland, Switzerland and Turkey. It won the 2008 MOJO Award for Song of the Year and the Ivor Novello Award for Most Performed Work, and it is Duffy's best-selling single and signature song.
