Exorcism
In Christianity, exorcism is the practice of casting out demons. In Christian practice the person performing the exorcism, known as an exorcist, is often a member of the Christian Church, or an individual thought to be graced with special powers or skills. The exorcist may use prayers and religious material, such as set formulas, gestures, symbols, icons, amulets, etc. The exorcist often invokes God, Jesus and/or several different angels and archangels to intervene with the exorcism. Protestant Christian exorcists most commonly believe the authority given to them by the Father, Son, and Holy Spirit (the Trinity) is the source of their ability to cast out demons.
Exorcism in Christianity
The traditional method for determining if a person needs a deliverance is done by having someone present who has the gift of discerning of spirits. This is a gift of the Holy Spirit from 1 Corinthians 12 that allows a person to "sense" in some way an evil presence. While the initial diagnosis is usually uncontested by the congregation, when many people are endowed with this gift in a single congregation, results may vary.