This chapter establishes a typology of the Dies Irae. Based on the author’s corpus of films that quote the melody, this typology is concerned with both the form and function of each musical reference. The first type, labeled the “Prelude to Evil,” features statements of the melody that unfold at least the first seven notes of the melody and always occur prior to something inherently evil, scary, or macabre. The largest subset of this category sees films that use the Dies Irae as part of their main titles sequence. The second type, called the “Ominous Echo,” restricts the melody to its first four notes; this incipit frequently occurs just after a shocking event, either a death or other sinister event. The final type, the “Tension Engine,” subjects the Type 2 incipit to one of two processes: either setting it in a constant state of repetition, much like an ostinato {OS}, or spinning it forth {FS} into melodic statement derived from the Dies Irae but no longer following the melody’s pattern. Regardless of the subtype, the reference normally occurs during an action sequence with the musical material generating energy to match the screen.