Mentally ill offenders have a right to a fair trial and adequate treatment in terms of the law. The diversion of mentally ill offenders between the criminal justice and the mental health care systems is linked to the forensic psychiatric assessment and based on two psycho-legal constructs, fitness to stand trial (FTST) and criminal responsibility (CR). Forensic psychiatric assessment is therefore an important element in criminal law and plays a major role in the court\'s decisions regarding the sentence, detention, placement, or treatment of mentally ill offenders. The legislation aims to ensure balancing the rights of mentally ill offenders to psychiatric care and society\'s safety. A narrative overview of the literature summarizing the findings on legislation regulating FTST and CR assessment and their practice in different areas of the world was conducted. It offers insight into the advantages and disadvantages of the various approaches and examines the way court proceedings function in these different geographical and psychosocial-legal contexts. This may have policy implications for individual systems and allow countries to consider feasible mechanisms to refine the relevant legislation to improve their practices in forensic psychiatric assessments. Worldwide, relevant legislation is considered as essential in protecting mentally ill offender\'s right; it has been established for many years regarding specifying the procedures and responsibilities for the mental health care and criminal justice systems. Despite similarities in the principles of the psycho-legal constructs in different countries, there are differences in the way legislations are implemented, often depending on the available resources.