The Rite by Matt Baglio

This is the book the movie was based on. Baglio is a journalist in Italy who spent years with Father Gary Thomas as he was trained to become an exorcist. The book provides an excellent, well-researched examination of the rite of exorcism, including its history, theology, the processes by which priests determine whether someone is actually possessed and not suffering from neurological or psychological problems which can have similar effects, and real cases.

One of the most surprising things I learned is that an exorcism is not a "one and done" event; it can go on for years, or even decades, with the victim of possession regularly receiving prayers and actual exorcisms every week or month. It becomes something to be managed, not cured, much like diabetes. The other notable fact (at least to me) was that demonic possession can happen not just to those of weak faith who dabble in the occult, but also very holy people and people who are "cursed." The latter in particular was surprising -- for all that I believe in God, I have a fairly strong scientific mindset and I don't believe in actual, working magics or curses. So realizing that many priests, at least in Italy, think curses are real was unexpected. More upsetting for me was the idea that a demonic possession can be caused by someone else; one of the worst cases described in the book was that of a woman cursed by her own mother in utero. This seems fundamentally unfair to me. I realize cancer is not fair either, nor a flood, and people can suffer abuse for years at the hands of others, but somehow this feels different. Despite the serious nature of the subject matter, however, I enjoyed it quite a bit; it was extremely informative and non-sensationalistic.

P.S. Don't read this if you are at all hypochondriacal, or you will be convinced that every headache, every flash of pain, every stray negative thought you have is actually caused by a demon. One night while reading it I had to stop for a few minutes to reassure and put back to bed a crying Beadboy2, who believed there were "scaries" in his room. 20 minutes later, I got to read about how one of the signs of possession for one woman (the one cursed by her mother) was the fact that as a child she felt there were monsters in her room, and she always buried herself under the covers like Beadboy2 does. That did not make for a restful night.