Although highly controversial, Hervey Cleckley's Mask of Sanity provides one of the most influential clinical descriptions of psychopathy in the 20th century. At the crux of his argument, Cleckley claims that many psychopathic personalities go undiagnosed because they maintain a social mask that conceals their mental disorder and enables them to blend in with society. Furthermore, many of these affected individuals appear to function normally in accordance with standard psychiatric criteria.

Intent on detecting and diagnosing the elusive psychopath, Cleckley has compiled an assortment of case studies and offers suggestions for palliative care. This ambitious work aims to define and examine every aspect of this abstract state of being. Ultimately, Cleckley refines the term "psychopath" and strips it of stigmatization.

This classic has transformed the psychiatric definition of sanity and continues to provide insight on American society and psychological introspection.