"Sweetest Sin" is a song by American singer Jessica Simpson. It was written by Diane Warren and produced by Ric Wake for Simpson's third studio album, In This Skin (2003). It was released as the album's first single on July 14, 2003 through Columbia Records. The R&B song, speaks about what would be the sweetest sin between a couple. "Sweetest Sin" received positive reviews from critics. Simpson performed the song on her Reality Tour Live (2004). An accompanying music video, directed by Constantine Paraskavopoulos, showed Simpson swaying on a beach and flirting with singer Nick Lachey during the whole video.