The study of crime, criminals, law enforcement, and punishment.
Example:
His growing interest in criminology led him to become a probation officer.
Criminology includes the study of all aspects of crime and law enforcement -- criminal psychology, the social setting of crime, prohibition and prevention, investigation and detection, apprehension and punishment. Thus, many of the people involved -- legislators, social workers, probation officers, judges, etc. -- could possibly be considered criminologists, though the word usually refers to scholars and researchers only.