A hallucination, in the broadest sense, is a perception in the absence of a stimulus. In a stricter sense, hallucinations are defined as perceptions in a conscious and awake state in the absence of external stimuli which have qualities of real perception, in that they are vivid, substantial, and located in external objective space. The latter definition distinguishes hallucinations from the related phenomena of dreaming, which does not involve wakefulness. This book gathers and presents research from around the globe in the study of hallucinations including the origin of hallucinations, auditory verbal hallucinations in schizophrenic patients, Charles Bonnet Syndrome, as well as hallucinations and suicide risk and the neurobiological basis of hallucinations.