Exorcism
In Catholic practice the person performing the exorcism, known as an exorcist, is an ordained priest. The exorcist recites prayers according to the rubrics of the rite, and may make use of religious materials such as icons and sacramentals. The exorcist invokes God—specifically the Name of Jesus—as well as members of the Church Triumphant and the Archangel Michael to intervene with the exorcism. According to Catholic understanding, several weekly exorcisms over many years are sometimes required to expel a deeply entrenched demon.
International Association of Exorcists
Although the membership is restricted and exclusive, by 2000 there were over two hundred members, who meet bi-annually in Rome. The association sends out a quarterly newsletter where members can tell of particularly interesting or difficult cases. An exorcist priest must have the permission of his bishop to join. 
Within the Roman Catholic Church a priest may only do an exorcism with the express consent of his bishop or local ordinary, and only, to the extent necessary, after an examination of the patient by doctors and psychiatrists in order to determine that the affliction has no natural origin. A priest is required by canon law to be devout, knowledgeable, prudent, and possess integrity of life.