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. Precise figures are very difficult to obtain (the Catholic Church, for example, does not publish official statistics for the number of exorcisms performed by its priests). What is known is that most large Catholic dioceses in North America have access to official exorcists, and these priests receive specialist training to undertake exorcism ministries. No official numbers are available (the Catholic Church does not identify priests who act as exorcists), but it is believed that in 2011, the Catholic Church had around 15 trained exorcists in North America. Today, that number is believed to be well over 100.

Perhaps not coincidentally, polls suggest that belief in demons and demonic possession is also rising. One poll conducted in 2019 in America found that 22% of those surveyed believed that demons "definitely exist" while a further 24% believe that such entities "probably exist." Those are staggering numbers in a modern, industrialized, advanced nation. Some people claim that belief in demons and demonic possession has never been higher.

Naturally, this increasing belief in demonic possession has also led to an increase in the numbers of exorcisms that priests and others are called to perform. Again, precise figures are not available, but one high-profile exorcist in America, Father Vincent Lampert, the exorcist for the Archdiocese of Indianapolis, told a reporter in October 2018 that he had received over 1,700 requests for exorcisms so far that year, the highest number he had ever experienced. Other Catholic priests trained in exorcism rites in North America had said that this aspect of their ministry has become so overwhelming that they can barely cope with requests for exorcisms.

All of this makes clear that the concepts of demonic possession and exorcism are not merely topics of interest to historians, but things that are affecting growing numbers of ordinary people around the world right now.