A modus operandi (often shortened to M.O.) is someone's habits of working, particularly in the context of business or criminal investigations, but also more generally. It is a Latin phrase, approximately translated as mode (or manner) of operating.
The term is often used in police work when discussing crime and addressing the methods employed by criminals. It is also used in criminal profiling, where it can help in finding clues to the offender's psychology. It largely consists of examining the actions used by the individuals to execute the crime, prevent its detection and facilitate escape. A suspect's modus operandi can assist in their identification, apprehension, or repression, and can also be used to determine links between crimes.
In business, modus operandi is used to describe a firm's preferred means of executing business and interacting with other firms.
The plural is modi operandi. The word operandi is a gerund in the genitive case, "of operating"; gerunds can never be pluralised in Latin, as opposed to gerundives. When a noun with an attribute in the genitive is pluralised, only the head noun normally changes, just as in English with "of": "a fact of life, two facts of life" (unlike, for instance, 'les modes opératoires' in French).
- Criminology – Study of the causes and manifestations of crime
- John E. Douglas – American criminal profiler
- Latin phrases
- Modus ponens – Rule of logical inference
- Modus tollens – Rule of logical inference
- Modus vivendi – An arrangement that allows conflicting parties to coexist in peace
- Signature crime
- Douglas, J. E. and A. W. Burgess, A. G. Burgess, R. K. Ressler. Crime classification manual (John Wiley & Sons, 2006) ISBN 0-7879-8501-5, p. 19-21.
- Vronsky, R. Serial Killers (Berkley Books, 2004) ISBN 0-425-19640-2, p. 412.
- Hazelwood, R. R, A. W. Burgess, Practical Aspects of Rape Investigation, (CRC Press, 2001) ISBN 0-8493-0076-2, p. 517.
- Berg, B.L. Criminal Investigation (McGraw Hill, 2008) ISBN 978-0-07-340124-9
- Barber, Katherine (ed.). "modus operandi". The Canadian Oxford Dictionary. Oxford University Press. ISBN 9780195418163. Retrieved 6 April 2020.
- The dictionary definition of modus operandi at Wiktionary