Diabolus in Musica (Latin for "The Devil in Music") is the eighth studio album by American thrash metal band Slayer, released on June 9, 1998 by American Recordings. Guitarist Jeff Hanneman wrote most of the album's content, which has been described as Slayer's most experimental. It was the band's first album to be played mostly in C♯ tuning, and named after a musical interval known for its dissonance. Lyrical themes explored on the album include religion, sex, cultural deviance, death, insanity, war, and homicide.
Despite receiving mixed reviews from critics, Diabolus in Musica peaked at number 31 on the Billboard 200, selling over 46,000 copies in its first week of sales. By 2006, it had sold over 290,000 copies in the United States.