In the 21st century, most people associate the idea of the possession of a person or place by a malevolent supernatural entity with the medieval world and particularly with the Catholic Church, but the truth is considerably stranger. Virtually every human culture that has ever existed has talked about both possession and exorcism, a rite or ritual used to free a person or place from possession. The terms used to describe the process of possession and entities thought to be responsible have changed throughout history, but the central theory does not. In certain circumstances, it is said that a person, place, or object may become inhabited by an entity that comes from somewhere else. The outcome is generally negative and sometimes even fatal. The only effective remedy is exorcism, the banishment of the entity involved to the place from which it came.

Some branches of modern psychology suggests that possession is simply a form of mental illness and that all these cases can be explained in psychological terms. But, as you will see, there appears to be a remarkable consistency in reports of possessions and even witness reports of possessed people demonstrating remarkable powers and abilities. It is difficult to explain those things purely in terms of psychology.

Furthermore, while people might associate possession and exorcism with the past, particularly the medieval world, claims have increased dramatically in the past 50 years. The situation became so serious that in 1990, a group of Roman Catholic priests formed the International Association of Exorcists (IAE). This group lobbied the Vatican to recognize the growth of instances in demonic possession, and in 2004, the Vatican's Congregation for the Doctrine of the Faith asked every Catholic diocese to appoint a trained exorcist.