Demonology is the systematic study and classification of demons and evil or unclean spirits, their names, natures, ranks, and dealings with humankind. Far from being a single tradition, it appears within many religions as the counterpart to angelology: an ordered account of the malevolent powers, the fallen angels and devils, set against the hosts of good.
In the Jewish and Christian traditions it developed out of the Second Temple period's elaboration of figures like the fallen Watchers of the Book of Enoch and the growing conception of Satan and his subordinates, and reached extraordinary complexity in the medieval and early modern West, where treatises and grimoires catalogued the demonic realm with bureaucratic precision, naming demons, assigning them ranks (princes, dukes, presidents of Hell), hours, and offices, and specifying the rites by which they might be summoned or repelled.
Works such as the Lesser Key of Solomon and Johann Weyer's Pseudomonarchia Daemonum enumerated the infernal hierarchy in detail. This literature stood in close and uneasy relation to the theology of exorcism and to the witch-hunts, in which demonological theory had lethal practical consequences. Comparable systems appear in Islamic accounts of the jinn and the shayatin, and in many other traditions. As a subject, demonology reveals how a culture imagines the sources of evil, temptation, and affliction, and how it maps, with sometimes disquieting thoroughness, the powers it most fears.