Criminal psychology is a field involving an amalgamation of psychology, criminology, and the law. This discipline was conceived in the mid-twentieth century, when psychologists began offering expert perspectives on criminal behaviour and speculate about the possible causes that push one to commit such acts. This chapter will expound upon the purview of criminal psychology, how it emerged as a specialized field of study, and how it is different from related disciplines such as forensic psychology. Further, this chapter will cover the role and responsibilities of a criminal psychologist in criminal justice proceedings as a clinician, experimentalist, actuarial, and advisor in criminal proceedings. It will also briefly encapsulate the role played by a criminal psychologist in investigation, trial, conviction, and rehabilitation of convicts. Then, next section will deal with scope of this field realized by different institutions and individuals globally, and what are the applications of this discipline in different countries of the world and India.