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
These exorcists routinely performed ceremonies over adults and infants preparing to be baptised. Authors such as Eusebius (3rd century) and Augustine (4th century) provide details of these minor exorcisms: Eusebius mentions the imposition of hands and prayer. Augustine noted that rites of exorcism by exsufflation (breathing upon the candidate) were also performed for the baptism of infants.