The fact that legal issues support local wisdom, ethics, and human rights and the way in which they operate in the nation-state are not well-understood; however, this is a significant issue. Indonesian independence, achieved on 17 August 1945, initiated substantial changes in the religious life of Indonesians. While most of Indonesia is Islamic, other religious beliefs include Hinduism and Christianity. Indonesia did not consider the Balinese a formal religious group in 1945. However, because of the Mount Agung eruption in Bali, many Balinese migrated outside the island. They lived in Lampung (Sumatra), certain places in Java, Palangkaraya (Borneo), Palu (Celebes), and other areas in the Indonesian archipelago, and have lived there for a long time. The total number of Balinese at the present day is around three million, but outside Bali, their number is 10 million. Their number increased throughout the Old Regime, the New Order, and the Reformation periods until the present time. They face many significant problems regarding the marriage and divorce laws juxtaposed with national law, as is the case with other religious communities, such as the Islamic community in Indonesia. Several important questions need to be addressed in this paper. First, what is adat law, or customary law, in Bali and outside Bali regarding the concept of Hindu Nusantara? Second, how should customary law be implemented, for example, relating to marriage and divorce issues in the building of the nation-state? Third, what is the customary law relating to the present situation of the Hindu communities in Indonesia? These are some significant questions. By using interdisciplinary approaches to customary laws, religious history, anthropology, and sociology, we expect to have a better understanding of how the Balinese customary law can become part of the formal law in modern Indonesia. By understanding these issues, it will be possible to strengthen national regulations by adopting certain values of customary law in modern Indonesia.