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 Christianity
The Catholic Church revised the Rite of Exorcism in January 1999, though the traditional Rite of Exorcism in Latin is allowed as an option. The act of exorcism is considered to be an incredibly dangerous spiritual task. The ritual assumes that possessed persons retain their free will, though the demon may hold control over their physical body, and involves prayers, blessings, and invocations with the use of the document "Of Exorcisms and Certain Supplications". In the modern era, Catholic bishops rarely authorize exorcisms, approaching would-be cases with the presumption that mental or physical illness is more likely.