This text explains what madness is, showing that it can be understood in psychological terms, and that by studying it we can learn important insights about the normal mind. It argues that traditional approaches to madness must be abandoned in favour of a new approach which is more consistent with what we now know about the human mind. Over the last 100 years or so it has become so commonplace to regard madness simply as a medical condition that it has become difficult to think of it in any other way. Bentall argues instead that delusions, hallucinations and other unusual behaviours are best understood psychologically, and that such experiences for the most part represent exaggerations of mental foibles to which we are all prone.