Persecutory delusions, the unfounded beliefs that others intend harm to the individual, are a major psychiatric problem. They are a common feature of severe mental illnesses such as schizophrenia, delusional disorder and bipolar disorder, often lead to admission to psychiatric hospital, and are a cause of considerable distress to patients and carers. However, increasingly it is recognised that persecutory delusions reflect the severe end of a spectrum of paranoia, which also encompasses beliefs and worries about threats from others that are common in the general population. In the last ten years an increasing number of researchers and clinicians have focussed on explaining paranoid experience in both clinical and non-clinical populations, with fascinating results. This recent research is presented for the first time as a book. In this landmark publication, the three major authorities in the field bring together the current knowledge about the assessment, understanding, and treatment of persecutory delusions. Leading experts in cognitive psychology, neuropsychology, psychiatry, social psychiatry, neuroimaging, and neuroscience explain their perspectives on paranoia. Pharmacological, cognitive, and family interventions are comprehensively reviewed, and personal accounts of paranoia are included.