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.
Exorcism
In Taoism, exorcisms are performed because an individual has been possessed by an evil spirit for one of two reasons. The individual has disturbed a ghost, regardless of intent, and the ghost now seeks revenge. An alive person could also be jealous and uses black magic as revenge thereby conjuring a ghost to possess someone. Members of the fashi, both Chinese ritual officers and priests ordained by a celestial master, perform Chinese rituals, in particular, exorcisms.