Writing, music, and recording
Slayer guitarist Jeff Hanneman described the writing process as, "When we were writing this album I was looking for something to beat; I wanted something to beat, but nothing impresses me right now. Nothing sounded really aggressive or heavy enough to inspire me to beat it, so I just had to come up with my own shit." The album was produced by Rick Rubin and was recorded at Oceanway Studios.
Adrien Begrand of PopMatters felt Slayer introduced characteristics to its music including tuned down guitars, murky chord structures, and churning beats. He believed these characteristics were adopted in response to the then-burgeoning nu metal scene. Drummer Paul Bostaph claims the album is his favorite as he thought the album was "as experimental as Slayer got". As a result, Diabolus in Musica was described as nu metal. The album is also has been described as groove metal and thrash metal. Bostaph returned to Slayer after his short-lived side project The Truth About Seafood, and the band entered the recording studio four months later.