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
The Catholic Church's Rite of Exorcism was revised in 1999. Paragraph 13 of its introduction states that a priest can be appointed by the local Bishop either for a single act of exorcism, or to the permanent position of 'exorcist'. The Rite then specifies that whenever it uses the word "exorcist" without qualification, it indicates a priest mandated in this way.
Among notable exorcists, Gabriele Amorth served as chief exorcist of the Diocese of Rome; he was the founder of the International Association of Exorcists.