<![CDATA[Abstract Customary law (hukum adat) is a set of living, evolving norms complied with by indigenous communities across Indonesia, even though most of it remains unwritten. Its existence is recognised constitutionally and reinforced through sectoral legislation, particularly in the regulation of communal land rights (hak ulayat) and the cultural identity of indigenous communities. Customary law possesses distinctive characteristics: it is local, flexible, grounded in cultural value, oriented toward the collective interest, and directed toward social harmony. In practice, social dynamics and overlapping interest frequently trigger customary conflict, whether between individuals within a single indigenous community, between indigenous communities, or between an indigenous community and a party outside that community, including the state and business actors. Resolution of customary conflict is generally pursued through customary adjudication (peradilan adat) emphasising the principles of restorative justice, communality, and social equilibrium. Customary adjudication functions as an important initial forum for dispute resolution, one that is more contextual, more legitimate in the community's eyes, and more socially accepted than formal litigation. The limited executory force of a customary decision, however, causes a portion of such conflict to be transferred to the national legal system. This article examines the legal and sociological consequences of that transfer, arguing that the transfer is best understood not as a wholesale displacement of customary authority but as a structurally necessary complement to it, activated specifically where customary adjudication's own institutional limits, principally its lack of coercive enforcement power, are reached. The study employs a normative legal method combining the statute approach and the conceptual approach. The findings show that the transfer brings a change in mechanism, sanction, and resolving actor, generating a positive effect in the form of legal certainty, alongside a negative effect in the form of the potential disruption of indigenous communities' social harmony, a tension this article argues can be substantially mitigated through a tiered, complementary institutional design connecting customary and national adjudication rather than treating them as competing systems.]]>
