There are a number of different ways that a person can (usually inadvertently) "invite" a demon to take possession of his/her body.

The Ouija Board is carte blanche for a demon, even when the board is being used to find the answers to seemingly harmless questions, like the name of a future spouse. The main problem here is that those using the Ouija Board don’t actually know what is answering their questions, nor how powerful the being may be. Many bookstores no longer sell Ouija Boards because of their ability to act as a portal for evil.

People at a low point in their lives, who may be feeling depressed, sad or desperate may harbour a desire to hand over responsibility for their lives to someone else. Demons construe this as a sign of weakness, and the added appeal is that a weak character is easy to control. Someone may wish that a situation or a person who is making their life difficult didn’t exist, and if the desire is strong enough a demon will oblige, and make the wishes come true – but there’s always a heavy price to pay.

Recently a belief receiving attention is the thought that a person may become possessed during an organ transplant; receiving a portion of the donor’s spirit during surgery. If the donor was a murderer or an evil person in life then there’s no telling how much of the malignant nature is passed to the recipient. And how will the recipient act? What aspects of the donor's character may be transferred to the recipient, and how will these manifest?

In medieval times it was thought Satan could possess someone in two different ways; either directly into the victim or through collaboration with a person wishing to harm the victim – such as a wizard or a witch. The elderly, the poor and the disfigured members of medieval society were often the victims of possession by the Devil, who was usually summoned by someone wishing to own the possessed person’s home or other property. Widows were often targeted in this way. People afflicted with terrible deformities, particularly of the face, were believed by many to suffer from the Mark of the Devil. Consider the case of John Remick, also known as The Elephant Man in 19th century London. Despite his terrible appearance he was a gentle, intelligent man who suffered years of humiliating, degrading treatment at the hands of a suspicious public.