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.
Exorcist
Since at least the third century, the Latin Church has formally ordained men to the minor order of exorcist. Text previously attributed to a fourth Council of Carthage (398), now identified as a collection called "Statuta Ecclesiæ Antiqua", prescribes in its seventh canon the rite of ordination of such an exorcist: the bishop is to give him the book containing the formulae of exorcism, saying, "Receive, and commit to memory, and possess the power of imposing hands on energumens, whether baptized or catechumens".