Possession is neither a new concept, nor a specifically Christian one. Throughout history, virtually all societies have recognized that it was possible for a man to be ‘taken over’ by an influence, or entity, outside himself. Two types of possession have been universally recognized: voluntary and involuntary possesion. It must be recognized that the majority of cases in which possession, or obsession, or even influence are alleged, can be explained in much simpler, psychological terms, and the terms relating to possession should be reserved only for cases in which all alternative explanations fail. Actual cases of possession, obsession and influence are exceptional; most alleged instances having alternative explanations. It should be remembered that exorcism itself, when performed in cases where there is no possession or obsession, can be a factor in causing the individual to be opened to all manner of undesirable influences.