Many people have encountered the terms “criminal signature” and “modus operandi” either on the news or in detective novels. Few, however, know that the two notions are not identical. While both terms are used to describe criminal behavior, each of them has a distinctive set of characteristics ( Offender’s signature vs. Modus Operandi, 2011). Every crime has a modus operandi, and a criminal signature, unique to the criminal that committed it. This distinction is used when analyzing criminals during police investigations, in order to understand how criminals operate and what motivates them ( Offender’s signature vs. Modus Operandi, 2011). These concepts are extensively used in modern criminology and victimology, and are particularly useful when investigating serial killers and rapists. This paper will cover the definitions of both terms, highlight key differences between them, describe the background and key driving forces behind modus operandi and criminal signature, and give the examples of both. Definitions Modus Operandi, or method of operation, describes conscious and deliberate actions taken by the criminal in order to commit a particular crime. It includes preparations and usage of items and tools, sequences of actions, times and dates of actions, etc. Modus operandi typically varies from one crime to another, since it includes actions tailored for particular situations ( Modus Operandi definition, 2016). For example, modus operandi of a criminal during a kidnapping may include the use of a gag to control the victim and prevent calling for help. Other examples include the use of gloves to avoid fingerprints, choosing to pursue victims after dark, or using a particular weapon to commit the crime. While the pattern may remain the same, it is prone to evolving as the criminal adapts to the changing circumstances and becomes more proficient in what he or she is doing. Thus, the main driving force behind modus operandi is the necessity, which depends on a criminal’s intellectual and physical characteristics, as well as on the availability of resources ( Modus Operandi definition, 2016). Criminal signature describes traits and elements of the crime scene that are largely unnecessary to the commitment of the crime, and serve for the criminal’s emotional or psychological gratification as a personal imprint ( Offender signature, 2016). These rarely change throughout repetitive cases and are often useful in studying and understanding the psychology of the perpetrator. In addition, this can be used to recognize whether or not the same criminal committed crimes. An example of a criminal signature includes the level of the victim’s injury – some criminals are meticulously accurate in their attacks, while others prefer to mutilate the victim. Leaving a note or an object at the crime scene, and collecting personal items from victims can also be used to form a crime signature for a particular criminal. Thus, the core motivations behind a criminal signature are strictly emotional ( Offender signature, 2016). Key Similarities and Differences Using the definitions given above, it is possible to outline a list of similarities and differences between the two notions: Similarities:   * Defining Modus Operandi and criminal signature of a criminal is significant and useful in linking crimes one to another.   * Both definitions include actions performed by the criminal dur