Exorcism (& Possession by Devils / Unclean Spirits)

The driving out of evil spirits in cases of demoniacal possession by adjuration. Such exorcism must be performed by a priest with the express permission of the bishop, and with the rite provided in the 'Rituale Romanium.' (Definition from A Catholic Dictionary, 1951)

Scripture has many, many references to people possessed by devils, and the removal of them. Everything in Scripture is written for our instruction. Exorcism has been used as needed throughout the history of the Catholic Church, so it is clear that possession by devils and unclean spirits has not been limited to the time of Jesus and the Apostles. See below for Scriptural references and past Church teaching.
 

References in Scripture to Possession by Devils / Unclean Spirits:

• "And when evening was come, they brought to him many that were possessed with devils: and he cast out the spirits with his word: and all that were sick he healed" Matthew 8:16
• "And when it was evening, after sunset, they brought to him all that were ill and that were possessed with devils. And all the city was gathered together at the door. And he healed many that were troubled with divers diseases; and he cast out many devils, and he suffered them not to speak, because they knew him." Mark 1:32-34
• "And when they were gone out, behold they brought him a dumb man, possessed with a devil. And after the devil was cast out, the dumb man spoke, and the multitudes wondered, saying, Never was the like seen in Israel" Mark 9:32-33
• "Then was offered to him one possessed with a devil, blind and dumb: and he healed him, so that he spoke and saw. And all the multitudes were amazed, and said: Is not this the son of David? But the Pharisees hearing it, said: This man casteth not out the devils but by Beelzebub the prince of the devils. And Jesus knowing their thoughts, said to them: Every kingdom divided against itself shall be made desolate: and every city or house divided against itself shall not stand. And if Satan cast out Satan, he is divided against himself: how then shall his kingdom stand? And if I by Beelzebub cast out devils, by whom do your children cast them out? Therefore they shall be your judges. But if I by the Spirit of God cast out devils, then is the kingdom of God come upon you." Mark 12:22-28
• "And there was in their synagogue a man with an unclean spirit; and he cried out, Saying: What have we to do with thee, Jesus of Nazareth? art thou come to destroy us? I know who thou art, the Holy One of God. And Jesus threatened him, saying: Speak no more, and go out of the man. And the unclean spirit tearing him, and crying out with a loud voice, went out of him. And they were all amazed, insomuch that they questioned among themselves, saying: What thing is this? what is this new doctrine? for with power he commandeth even the unclean spirits, and they obey him." Mark 1:23-27
• "And as he went out of the ship, immediately there met him out of the monuments a man with an unclean spirit, Who had his dwelling in the tombs, and no man now could bind him, not even with chains. For having been often bound with fetters and chains, he had burst the chains, and broken the fetters in pieces, and no one could tame him. And he was always day and night in the monuments and in the mountains, crying and cutting himself with stones. And seeing Jesus afar off, he ran and adored him. And crying with a loud voice, he said: What have I to do with thee, Jesus the Son of the most high God? I adjure thee by God that thou torment me not. For he said unto him: Go out of the man, thou unclean spirit. And he asked him: What is thy name? And he saith to him: My name is Legion, for we are many." Mark 5:2-9
• "And when he was come forth to the land, there met him a certain man who had a devil now a very long time, and he wore no clothes, neither did he abide in a house, but in the sepulchers. And when he saw Jesus, he fell down before him; and crying out with a loud voice, he said: What have I to do with thee, Jesus, Son of the most high God? I beseech thee, do not torment me. For he commanded the unclean spirit to go out of the man. For many times it seized him, and he was bound with chains, and kept in fetters; and breaking the bonds, he was driven by the devil into the deserts. And Jesus asked him, saying: What is thy name? But he said: Legion; because many devils were entered into him." Luke 8:27-30
• "And lo, a spirit seizeth him, and he suddenly crieth out, and he throweth him down and teareth him, so that he foameth; and bruising him, he hardly departeth from him. And I desired thy disciples to cast him out, and they could not. And Jesus answering, said: O faithless and perverse generation, how long shall I be with you, and suffer you? Bring hither thy son. And as he was coming to him, the devil threw him down, and tore him. And Jesus rebuked the unclean spirit, and cured the boy, and restored him to his father." Luke 9:39-43
• "And his fame went throughout all Syria, and they presented to him all sick people that were taken with divers diseases and torments, and such as were possessed by devils, and lunatics, and those that had palsy, and he cured them" Matthew 4:24
• "Now some also of the Jewish exorcists who went about, attempted to invoke over them that had evil spirits, the name of the Lord Jesus, saying: I conjure you by Jesus, whom Paul preacheth" Acts 19:13
• "Finally, brethren, be strengthened in the Lord, and in the might of his power. Put you on the armor of God, that you may be able to stand against the deceits of the devil. For our wrestling is not against flesh and blood; but against principalities and power, against the rulers of the world of this darkness, against the spirits of wickedness in the high places. Therefore take unto you the armor of God, that you may be able to resist in the evil day, and to stand in all things perfect." Ephesians 6:10-13
• "And one of the multitude, answering, said: Master, I have brought my son to thee, having a dumb spirit. Who, wheresoever he taketh him, dasheth him, and he foameth, and gnasheth with the teeth, and pineth away; and I spoke to thy disciples to cast him out, and they could not. Who answering them, said: O incredulous generation, how long shall I be with you? how long shall I suffer you? bring him unto me. And they brought him. And when he had seen him, immediately the spirit troubled him; and being thrown down upon the ground, he rolled about foaming. And he asked his father: How long time is it since this hath happened unto him? But he said: From his infancy: And oftentimes hath he cast him into the fire and into waters to destroy him. But if thou canst do any thing, help us, having compassion on us. And Jesus saith to him: If thou canst believe, all things are possible to him that believeth. And immediately the father of the boy crying out, with tears said: I do believe, Lord: help my unbelief. And when Jesus saw the multitude running together, he threatened the unclean spirit, saying to him: Deaf and dumb spirit, I command thee, go out of him; and enter not any more into him. And crying out, and greatly tearing him, he went out of him, and he became as dead, so that many said: He is dead. But Jesus taking him by the hand, lifted him up; and he arose. And when he was come into the house, his disciples secretly asked him: Why could not we cast him out? And he said to them: This kind can go out by nothing, but by prayer and fasting" Mark 9:16-28
   

Church Teaching on Exorcism and Possession:

• The third order is that of exorcists, to whom is given the power to invoke the name of the Lord over those who are possessed by unclean spirits. Hence the Bishop when ordaining them presents to them a book in which the exorcisms are contained, and at the same time pronounces this form of words: Take, and commit to memory, and have the power of imposing hands over the possessed, whether baptised or catechumen." Catechism of Council of Trent, Sacrament of Holy Orders, Exorcist
• "But as to baptized persons who are vexed in body by unclean spirits, the same reason holds good of them as of others who are demented. Hence Cassian says (Collat. vii): "We do not remember the most Holy Communion to have ever been denied by our elders to them who are vexed by unclean spirits."" St. Thomas Aquinas, Summa Theologica, Is Communion to be given to those who lack the use of reason?
• "But the influence of the demon, as we know from Scripture and the history of the Church, goes further still. He may attack man's body from without (obsession), or assume control of it from within (possession). As we gather from the Fathers and the theologians, the soul itself can never be "possessed" nor deprived of liberty, though its ordinary control over the members of the body may be hindered by the obsessing spirit (cf. St. Aug., "De sp. et an.", 27; St. Thomas, "In II Sent.", d. VIII, Q. i; Ribet, "La mystique divine", Paris, 1883, pp. 190 sqq.)" 1917 Catholic Encyclopedia, Demonical Possession
• "All through the Middle Ages councils continued to discuss the matter: laws were passed, and penalties decreed, against all who invited the influence of the Devil or utilized it to inflict injury on their fellowmen (cf. the Bulls of Innocent VIII, 1484; Julius II, 1504; and Adrian VI, 1523); and powers of exorcism were conferred on every priest of the Church. The phenomenon was accepted as real by all Christians" 1917 Catholic Encyclopedia, Demonical Possession
• "Why possession should manifest itself in one country rather than another, why it should have been so common in the time of Christ and so comparatively rare in our own, why even in Palestine it should have been confined almost entirely to the province of Galilee are questions on which theologians have speculated but on which no sure conclusion can ever be reached. The phenomenon itself is preternatural; a humanly scientific explanation is, therefore, impossible." 1917 Catholic Encyclopedia, Demonical Possession

Summary

Jesus and His Disciples frequently speak of possession, and so has the Church in every year of every century, so there is no doubt that such a phenomena exists. Certainly possession is not as common in our day, and there are also instances where a medical condition may be mistaken for possession and vice versa, but this does not take away from the fact that demonic possession, and the need for exorcism, exists.

In our day, it appears cases of possession are most common among people who involve themselves in the occult, witchcraft, and the like.