Delusions, in their many different manifestations, are central to the concepts of madness and psychosis. Yet what causes them remains in many ways a complete mystery. McKenna’s Delusions is the first comprehensive attempt to tackle one of the most arresting phenomena in psychiatry: an in-depth and critical review of what delusions are, the forms they can take and how they might be explained from both psychological and biological perspectives. Delusions covers key topics such as the clinical features of delusions, the disorders they are seen in, other oddities that resemble them in both health and disease, and the different approaches that have been taken to try to understand them. It is an essential book for psychiatrists and psychologists who work with delusional patients, as well as being of interest to neuroscientists engaged in research into major psychiatric disorders.