Demonology (from Greek δαίμων, daimōn, "demon"; and -λογία, -logia) is the systematic study of demons or beliefs about demons. Insofar as it involves exegesis, demonology is an orthodox branch of theology. It is the branch of theology relating to superhuman beings who are not gods. It deals both with benevolent beings that have no circle of worshippers or so limited a circle as to be below the rank of gods, and with malevolent beings of all kinds. The original sense of "demon," from the time of Homer onward, was a benevolent being; but in English the name now holds connotations of malevolence.

Demons, when regarded as spirits, may belong to either of the classes of spirits recognized by primitive animism; that is to say, they may be human, or non-human, separable souls, or discarnate spirits which have never inhabited a body. A sharp distinction is often drawn between these two classes, notably by the Melanesians, the West Africans, and others; the Arab djinn, for example, are not reducible to modified human souls; at the same time these classes are frequently conceived as producing identical results, e.g. diseases. Demonology, though often referred to with negative connotation, was not always seen as evil or devilish as the term would have one believe.