This article documents and reviews customary practices and land concepts in the Philippines and examines the interface between state laws and customary laws within the context of the conflicts over indigenous peoples’ lands. The article employs case studies to discuss the application of state laws to indigenous peoples’ communities. It examines the interaction of the formal legal system with the customs and traditions the indigenous peoples have historically relied upon to dictate the rules regulating the use and alienability of land. Particular attention is devoted to the Cordillera experience in order to illustrate how community-level efforts to defend indigenous territories can operate either as a mechanism for reform within the state’s existing formal legal framework or as a means of challenging current legal texts and principles at their foundation.