Exorcism
In Catholic Christianity, exorcisms are performed in the name of Jesus Christ. A distinction is made between a formal exorcism, which can only be conducted by a priest during a baptism or with the permission of a bishop, and "prayers of deliverance" which can be said by anyone.
The Catholic rite for a formal exorcism, called a "Major Exorcism", is given in Section 11 of the Rituale Romanum. The Ritual lists guidelines for conducting an exorcism, and for determining when a formal exorcism is required. Priests are instructed to carefully determine that the nature of the affliction is not actually a psychological or physical illness before proceeding.
Unclean spirit
Exorcism is the most thoroughly attested Jewish magical practice of the Second Temple period. The exorcistic technique of fumigation by incense depends on the aerial conception of the unclean spirit: the occupation of air by odor or smoke (i.e., airborne particulate matter) was supposed to drive off or displace an unclean spirit. Since either body or soul could be unclean, it can be difficult to distinguish exorcism from traditional magico-medical practice in which a personified illness is adjured to depart from the patient's body (for instance, "Flee, Fever!") by means of a charm, spoken or inscribed on an amulet or other ritual object. In some rabbinic literature, demons are viewed as inflicting evil on humans in part through illness and disease, though Mishnah and Tannaitic scholars in Palestine did not view demons as the cause of illness.