The origins of offender classification, which is essentially the examination of how offenders differ from one another, can be traced to a typology presented by Cesare Lombroso in his 1876 work entitled Criminal Man. Development of structured instruments for ranking offenders according to risk began in the 1920s, when researchers such as Burgess (1928) explored the utility of statistical methods to distinguish between violators and non-violators among prisoners paroled from state prisons. Though numerous practitioners, criminologists, and forensic psychologists advanced classification research following this time, it was not until the 1980s that formal, structured classification became widespread practice in corrections. Three factors—the discovery that a relatively small proportion of offenders contributed disproportionately to the crime problem, successful inmate litigation calling for improved conditions of confinement in state prison systems, and heightened sensitivity of the public to new crimes committed by offenders released back into the community—accelerated the development and widespread adoption of objective instruments to classify offenders by risk and needs. Today, offender classification is practiced by local, state, and federal corrections agencies throughout the United States. There are now many instruments available for the classification of adult and juvenile offenders, and work on improving prediction of recidivism via statistical methods continues as a focus of agency and university research.