Background and Objective: The personality dossier is an important institution in modern criminal law, aimed at identifying the individual, psychological, familial, social, and criminal characteristics of defendants or convicted persons. It contributes to the individualization of criminal sanctions and the realization of criminal justice. Despite its recognition in Iranian criminal law, ambiguities remain regarding its dimensions, preparation, and application in criminal proceedings. This study comparatively examines personality dossiers in Iranian and French criminal law, identifying their similarities, differences, and potential implications for improving the Iranian legal system.This research adopts a descriptive-analytical and comparative approach, drawing on library resources, legislation, legal practices, and authoritative Persian and international literature.The findings indicate that both legal systems recognize the importance of understanding offenders’ personalities in achieving individualized criminal justice. However, French criminal law demonstrates greater coherence in identifying personality dimensions, involving specialized professionals, incorporating behavioral sciences, and continuously utilizing personality information throughout criminal proceedings and sentence enforcement. In contrast, although Iranian criminal procedure legislation provides for personality dossiers, legislative limitations, inadequate implementation infrastructure, and inconsistent practices restrict their effectiveness. Accordingly, improving the application of personality dossiers in Iran requires strengthening institutional infrastructure, expanding interdisciplinary cooperation, developing specialized guidelines, and selectively adapting relevant French legal experiences to Iran’s legal framework. Such reforms could enhance individualized sentencing, improve judicial decision-making, and promote a more effective, fair, and rehabilitative criminal justice system while ensuring that assessments of offenders’ personal circumstances remain consistent with fundamental legal principles and procedural safeguards.