Little difficulty in identifying the perpetrator of the harmful act, and the existence or absence of a causal relationship between the act and the damage can be determined with relative ease. However, when multiple factors contribute to the occurrence of the harm and several agents are involved, the matter becomes significantly more complex and important. This issue constitutes one of the more intricate topics in civil liability law. On one hand, it is necessary to distinguish the liable parties among the multiple contributing factors; on the other hand, it must be determined how the injured party may seek redress from the various actors, as well as the extent of each party’s liability. This requires the existence of clear and well-defined legal standards and criteria, to both prevent the issuance of contradictory judgments and ensure that no damage remains uncompensated. More importantly, compensation must be awarded in a fair and equitable manner so as to avoid injustice. Nevertheless, determining the appropriate method for achieving fair compensation in cases involving multiple contributing causes remains one of the most challenging issues in the field of civil liability law. This study explores the aforementioned subjects through a descriptive-analytical approach, based on statutory provisions, the views of Islamic jurists (fuqahā), and legal doctrine, with a comparative perspective between Iranian law and the Principles of European Tort Law (PETL), in order to highlight the similarities, differences, and existing gaps within the Iranian legal system.