Demonic possession is held by many belief systems to be the control of an individual by amalevolent supernatural being. Secularists generally consider all such claims to be manifestations of a mental disorder. Descriptions of demonic possessions often include erasedmemories or personalities, convulsions, “fits” and fainting as if one were dying. Other descriptions include access to hidden knowledge (gnosis) and foreign languages (glossolalia), drastic changes in vocal intonation and facial structure, the sudden appearance of injuries (scratches, bite marks) or lesions, and superhuman strength. Unlike in channeling or other forms of possession, the subject has no control over the possessing entity and so it will persist until forced to leave the victim, usually through a form of exorcism.
Many cultures and religions contain some concept of demonic possession, but the details vary considerably. The oldest references to demonic possession are from the Sumerians, who believed that all diseases of the body and mind were caused by "sickness demons" called gidim or gid-dim. The priests who practiced exorcisms in these nations were called ashipu (sorcerer) as opposed to an asu(physician) who applied bandages and salves. Many cuneiform tablets contain prayers to certain gods asking for protection from demons, while others ask the gods to expel the demons that have invaded their bodies.
Shamanic cultures also believe in demon possession and shamans perform exorcisms. In these cultures, diseases are often attributed to the presence of a vengeful spirit (or loosely termed demon) in the body of the patient. These spirits are more often the spectres of animals or people wronged by the bearer, the exorcism rites usually consisting of respectful offerings or sacrificial offerings.
- "In the Old Testament we have only one instance, and even that is not very certain. We are told that "an evil spirit from the Lord troubled" Saul (1 Samuel 16:14). The Hebrew rûah need not imply a personal influence, though, if we may judge from Josephus(Ant. Jud., VI, viii, 2; ii, 2), the Jews were inclined to give the word that meaning in this very case. In New-Testament times, however, the phenomenon had become very common."
- Matthew 4:23-25: Demon-possessed persons are healed by Jesus (also Luke 6:17-19).
- Matthew 7:21-23: Many will drive out demons in Jesus' name (also Mark 16:17; Luke 10:17; Acts 5:16; 8:7).
- Matthew 8:14-17: Jesus healed many demon-possessed (also Mark 1:29-39; Luke 4:33-41).
- Matthew 8:28-34: Jesus sent a herd of demons from two men into a herd of pigs ("about two thousand" pigs, according to the account at Mark 5:1-20; both Mark's account and Luke 8:26-39, mention only the one man).
- Matthew 9:32-34: Jesus made a demon-possessed mute man speak, the Pharisees said it was by the power of Beelzebub (also Mark 3:20-22).
- Matthew 10:1-8: The Twelve Apostles given the authority to drive out evil spirits (also Mark 3:15; 6:7; 6:13; Luke 9:1;10:17).
- Matthew 11:16-19: "this generation" said that John the Baptist was possessed by a demon (also Luke 7:31-35).
- Matthew 12:22-32: Jesus healed a demon-possessed blind and dumb man (also Luke 11:14-23; 12:10; Mark 3:20-30).
- Matthew 12:43-45: Jesus told an allegory of nasty spirits coming back home, that is, to the human body where they have lived before (also Luke 11:24-26).
- Matthew 15:21-28: Jesus expelled a demon from the body of the daughter of a Canaanite woman (also Mark 7:24-30).
- Matthew 17:14-21: Jesus healed a lunatic by driving out a demon from him (also Mark 9:14-29; Luke 9:37-49).
- Mark 1:21-28: Jesus expelled a nasty spirit from a man (also Luke 4:31-37).
- Mark 9:38-40: A non-Christian is seen driving out demons in Jesus' name (also Luke 9:49-50).
- Mark 16:9: Jesus had driven seven demons out of Mary Magdalene (also Luke 8:2).
- Luke 7:21: Many people are cleansed from evil spirits by Jesus.
- Luke 13:10-17: Jesus expelled a spirit of disease from the body of a woman on the Sabbath.
- Luke 13:31-32: Jesus continued to cast out demons even though Herod Antipas wanted to kill him.
- Luke 22:3: Satan entered into Judas Iscariot (also John 13:27).
- John 7:20: A "crowd of Jews" that wanted to kill Jesus said he was demon-possessed.
- John 8:48-52: "The Jews" said Jesus was a Samaritan and demon-possessed.
- John 10:20-21: Many Jews said Jesus was raving mad and demon-possessed, others said he was not.
- Acts 5:3: Satan filled the heart of Ananias.
- Acts 5:16: The Apostles healed those tormented by evil spirits.
- Acts 8:6-8: At the teaching of Philip the Evangelist in Samaria, evil spirits came out of many.
- Acts 8:18-19: Simon Magus offered to buy the power of Laying on of hands.
- Acts 10:38: St. Peter said Jesus healed all who were under the power of the devil.
- Acts 16:16-24: Paul and Silas were imprisoned for driving a future-telling spirit out of a slave girl.
- Acts 19:11-12: Handkerchiefs and aprons touched by Paul cured illness and drove out evil spirits.
- Acts 19:13-20: Seven sons of Sceva attempted to drive out evil spirits by saying: "In the name of Jesus, whom Paul preaches, I command you to come out." But because they did not have faith in Jesus, they were unsuccessful and were actually driven from that house by the possessed.
- Revelation 18:2: The Whore of Babylon is a home for demons, evil spirits and unclean birds.
Acts of the Apostles contains also a number of references to people coming under the influence of the Holy Spirit (1:8, 2:4, 2:17-18,2:38, 4:8, 4:31, 6:3-5, 7:55, 8:15-19, 8:39, 9:17, 10:19, 11:12-16, 11:28, 13:9, 16:6-7, 19:2-6, 20:23,21:11, 23:8-9) which is believed to be a good thing in contrast to demonic influence, see also Spirit possession#Christianity.
The 1902 work Demonic possession in the New Testament by Rev. William Menzies Alexander attempted to explain accounts of possession in the synoptic Gospels, outlining their historical, medical and theological aspects.exorcism
The Bible clearly indicates that people can be possessed by demons but that the demons respond to Jesus's authority.
In the synagogue there was a man possessed by a demon, an evil spirit. He cried out at the top of his voice, 34 “Ha! What do you want with us, Jesus of Nazareth? Have you come to destroy us? I know who you are—the Holy One of God!” 35 “Be quiet!” Jesus said sternly. “Come out of him!” Then the demon threw the man down before them all and came out without injuring him. 36 All the people were amazed and said to each other, “What is this teaching? With authority and power he gives orders to evil spirits and they come out!” 37 And the news about him spread throughout the surrounding area. (Luke 4:33-35 NIV)
It also indicates that demons can possess animals.
When Jesus stepped ashore, he was met by a demon-possessed man from the town. For a long time this man had not worn clothes or lived in a house, but had lived in the tombs. 28 When he saw Jesus, he cried out and fell at his feet, shouting at the top of his voice, “What do you want with me, Jesus, Son of the Most High God? I beg you, don’t torture me!” 29 For Jesus had commanded the impure spirit to come out of the man. Many times it had seized him, and though he was chained hand and foot and kept under guard, he had broken his chains and had been driven by the demon into solitary places. “Legion,” he replied, because many demons had gone into him. 31 And they begged Jesus repeatedly not to order them to go into the Abyss. 32 A large herd of pigs was feeding there on the hillside. The demons begged Jesus to let them go into the pigs, and he gave them permission. 33 When the demons came out of the man, they went into the pigs, and the herd rushed down the steep bank into the lake and was drowned. (Luke 8:27-32 NIV)
The literal view of demonization is still held by a number of Christian denominations. Official Catholic doctrine affirms that demonic oppression can occur as distinguished from mental illness, but stresses that cases of mental illness should not be misdiagnosed as demonic influence. Catholic exorcisms can occur only under the authority of a bishop and in accordance with strict rules; a simple exorcism also occurs during Baptism (CCC 1673). In charismatic Christianity, deliverance ministries are activities carried out by individuals or groups aimed at solving problems related to demons and spirits, especially possession of the body and soul, but not the spirit as ministries like Ellel Ministries International, Don Dickerman Ministries and Neil T. Anderson explicitly teach that a Christian can not have demons in their spirit because the Holy Spirit lives there, though they can have demons in their body or soul due to inner emotional wounds, sexual abuse, satanic ritual abuse.  This is usually known as partial possession or demonic infestation, as opposed to outside demonic oppression which does not reside in any of the 3 parts of a person: body, soul, spirit.
A great deal of controversy surrounds the book War on the Saints originally published in 1912 as a resource to the Christian faced with combating demon influences.
In the New Testament Jesus is reported to have encountered people who were demonized and to have driven the "evil spirits" out of these demoniacs. In the 4th century, St. Hillary asserted that demons entered the bodies of humans to use them as if they were theirs, and also proposed that the same could happen with animals.
The New Testament's description of people who had evil spirits includes a capacity for hidden knowledge (e.g., future events, innermost thoughts of the people around them) (Acts 16:16) and great strength (Act 19:16), among others, and shows those with evil spirits can speak of Christ (Acts 19:16, Mark 3:11). According to Catholic theologians, demonic assault can be involuntary and allowed by God to test a person (for more details about God's tests on persons see Job). Involuntary demonic assault, according to these theologians, cannot be denied because this would imply the negation of the cases mentioned in the New Testament (12, some of them repeated in more than oneGospel). However, in the overwhelming majority of cases of alleged demonic possession in modern times, the victim can suffer due to any of a number of personal initiatives: occult practices, mortal sin, loss of faith, or psychological trauma, among others.
In previous centuries, the Christian church offered suggestions on safeguarding one’s home. Suggestions ranged from dousing a household with Holy water, placing wax and herbs on thresholds to “ward off witches occult,” and avoiding certain areas of townships known to be frequented by witches and Devil worshippers after dark.
Demonic possession is not recognized as a psychiatric or medical diagnosis by either the DSM-IV or the ICD-10. There are many psychological ailments commonly misunderstood as demonic possession, particularly dissociative identity disorder. In cases of dissociative identity disorder in which the alter personality is questioned as to its identity, 29% are reported to identify themselves as demons, but doctors see this as a mental disease called demonomania or demonopathy, a monomania in which the patient believes that he or she is possessed by one or more demons.
- Aix-en-Provence possessions
- Johann Blumhardt
- Clara Germana Cele
- Antoine Gay
- Loudun possessions
- Louviers possessions
- George Lukins
- Robbie Mannheim (Roland Doe)
- Anneliese Michel
- Michael Taylor (Ossett)
- A well-known work on the subject is the 1973 film The Exorcist, based on the book of the same name, which portrays a case of demonic possession. The book was inspired by an actual real-life case of exorcism involving Robbie Mannheim. This was continued in the 1990 sequel The Exorcist III, and the prequel, Exorcist: The Beginning from 2004 and the original cut of the film, Dominion: Prequel to the Exorcist which was released on DVD in 2005.