Modus operandi (often used in the abbreviated form MO) is a Latin phrase, approximately translated as "mode of operation." The plural is modi operandi ("modes 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 English in a non-criminal sense to describe someone's habits or manner of working, the method of operating or functioning.
A criminal's MO may also be used in offender profiling, where it can also be used to find clues to the perpetrator's psychology.
The method of operation or MO is sometimes confused with a criminal's "signature". While a criminal's MO may change over time, his or her signature will usually stay the same.