The term "modus operandi" or MO is derived from two Latin phrase nuodo operandi, literally meaning “mode of functioning”. Generally, an MO refers to the technique an individual or group uses to commit a crime or plan a criminal operation, although the phrase is also commonly used to refer to the distinct behavior characteristic of a particular individual or organization. It is similar to a "signature evidence" which is the unique characteristics that, together with other identifying features, can be used to recognize a criminal.

The modus operandi of criminals is a closely studied area, with investigators and law enforcement personnel devoting significant time and resources to identifying and profiling criminal activities. By studying and understanding a subject's MO, investigators can gain important information about their criminal activities, such as the level of violence used, the types of targets selected, and the manner in which a crime is conducted. For example, a criminal who commits robberies with a certain level of violence on a certain demographic may be easy to identify by law enforcement.

In order to effectively study an individual or group's modus operandi, forensic scientists and other professionals must closely analyze evidence and any available information regarding the criminal activity. Investigators will focus on identifying the methods employed, the timeframe in which the activity occurred, and other information related to the activities. In particular, they may look at the type of weapon used, the type of entry gained into the building, and any distinct behaviors during the incident. By carefully examining the available evidence, law enforcement personnel and forensic scientists can develop a profile of an individual or group's MO and use it to identify suspects or create preventive strategies.

The most common crime areas where modus operandi is used includes robbery, murder, burglary and white-collar crime. A study of criminal mo's helps to identify the crime patterns in different places. For example, analysing the modus operandi of robbery in an area can help to provide a clear picture of the motives involved, the style of the burglar and the tendency of the thief to use the same tactics. This can also help to predict future crimes by allowing law enforcement to look for similar MOs in different cases.

By understanding a person's MO, forensic scientists and law enforcers can build a clear picture of the criminal activities of an individual or group, aiding in the investigation and prevention of future crimes. Modus operandi can also be used in non-criminal contexts, such as the stock market, in order to make predictions and analyze trends. A person’s MO can be a powerful tool in solving and preventing crimes by providing law enforcement with the ability to recognize, profile and predict the behavior of criminals.