Diabolus in Musica 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.