"Sweetest Sin" is a song by American recording artist 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 22, 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, with some calling it a catchy tune and an "ode to booty knocking".