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.
The Exorcist
The Exorcist is a 1973 American supernatural horror film directed by William Friedkin, adapted by William Peter Blatty from his 1971 novel of the same name, and starring Ellen Burstyn, Linda Blair, Max von Sydow, and Jason Miller. The film is part of "The Exorcist" franchise. The book, inspired by the 1949 exorcism of Roland Doe, deals with the demonic possession of a 12-year-old girl and her mother's attempts to win back her child through an exorcism conducted by two priests. The adaptation is relatively faithful to the book, which itself has been commercially successful (hitting the "New York Times" bestseller list).