This book is based upon twenty-three years experience in local and convict prisons, and more particularly upon the work done, during the past three years, with offenders from Courts in Birmingham and the adjacent districts. The main object is to demonstrate how important is the throrough examination of the individual offender, especially in regard to his mentality. It is only by a great extension of this line of investigation that we can hope to solve the problems which criminality presents. A considerable part of the book is devoted to that new development of psychology which is known as psycho-analysis, and to the possible applications thereof to the investigation and treatment of offenders. The book includes a brief description of the theory and technique of psycho-analysis, so that the reader may not have to look elsewhere for an explanation of technical terms.