Book excerpt: “Either you believe in possession or you do not. It is that simple, or at least that is how it often seems. However, the existence of the possession state in the human condition is not a matter of faith, it is a phenomenon that demands exploration.” So begins the introduction of this psycho-spiritual exploration of involuntary (or demonic) possession. Avoiding the pitfalls of many such works, here is presented the inarguable fact that the possession state does occur and must be taken seriously if those who are afflicted are to be helped. The only argument that remains is the attributed cause of the state. Covering a comprehensive array of topics from the history of demonic possession to a present understanding of the phenomenology and intrapsychic dynamics of the possession state, the book also provides a depth of understanding with respect to the various forms of possession encountered throughout the world. Readers will also gain an understanding of the various cultural and psychological explanations for possession, including neuropsychological, hypnosis, and psychodynamic theories. It concludes with the examination of three cases of demonic possession and the presentation of diagnostic criteria to assist in differentiating possession from common forms of psychopathology.