Codex Saerus: The Black Book of Satan, published by the Order of Nine Angles (ONA/O9A), is classified under the genres of Occultism, Satanism, and specifically Traditional Satanism or the Left-Hand Path. It is a foundational text of the ONA and is recognized as a grimoire that outlines ritual workings, including the "sinister" philosophy of the Order, black masses, and initiation ceremonies.