This study aims to formulate a model for harmonizing Islamic inheritance law and the Indonesian Civil Code based on the principles of justice and legal certainty. Indonesia has a pluralistic legal system that encompasses Islamic law, customary law and Western civil law, thus giving rise to dualism of norms, conflicts of inheritance rights and the practice of choosing judicial authority subdivisions. Islamic inheritance law emphasizes substantive justice through the faraidh system, while the Civil Code emphasizes individual freedom through testamentary freedom, so that these differences in principle create tensions between distributive justice and formal justice, as well as between legal certainty and legal flexibility. The study uses normative methods with legislative, conceptual and comparative approaches, as well as qualitative analysis of primary, secondary, and tertiary legal materials. The results of the study indicate the need for harmonization of inheritance law through three levels: normative integration of the principles of substantive justice and legal certainty, preparation of systematic national regulations and implementation of empowering judges in the application of progressive law. The paper offers a conceptual contribution in the form of an adaptive and applicable model of harmonization of inheritance law, as well as practical recommendations for regulatory.
