Modus operandi (often used in the abbreviated form MO) is a Latin phrase, approximately translatable as "mode of operation." It is used in police work to describe a criminal's characteristic patterns and style of work. The term is also commonly used in the United States of America in a non-criminal sense to describe someone's habits. Latin is the language originally spoken in the region around Rome called Latium. ... In statistics, the mode is the value that has the largest number of observations, namely the most frequent value or values. ... for other uses please see Crime (disambiguation) A crime is an act that violates a political or moral law. ... A habit is the usual condition or state of a person or thing, either natural or acquired, regarded as something had, possessed, and firmly retained. ...

A modus operandi can be used to narrow down an investigation amongst a group of criminals. For example, a burglar may typically use a back window, broken with a rock. If one of a group of known criminals is suspected to have committed a burglary, then their characteristic MOs can be compared to help identify the burglar.

A criminal's MO can also be used in profiling, where it can be used to find clues to the perpetrator's psychology.