The 1945 Constitution is the highest legal authority in Indonesia, of which executive, legislative and judicial branches of government must defer to it. The constitution was written in July and August 1945, when Indonesia was emerging from Japanese control at the end of World War II. It was abrogated by the Federal Constitution of 1949 and the Provisional Constitution of 1950, but restored after the President Sukarno's decree on July 5, 1959. During the 32 years of Suharto's administration, the constitution had never been amended. Suharto refused to countenance any changes to the constitution and the People's Consultative Assembly passed a law in 1985 requiring national referendum for the constitution amendments.

Indonesia legislation come in different forms. The following official hierarchy of Indonesia legislation (from top to bottom)is enumerated under Law No. 10 Year 2004 on the Formulation of Laws and Regulations:

1. 1945 Constitution (Undang-Undang Dasar 1945 or UUD'45)
2. Law (Undang-Undang or UU)and Government Regulation in Lieu of Law (Peraturan Pemerintah Pengganti Undang-Undang or Perpu)
3. Government Regulation (Peraturan Pemerintah or PP)
4. Presidential Regulation (Peraturan Presiden or Perpres)
5. Regional Regulation (Peraturan Daerah or Perda)

Law of Indonesia is based on a civil law system, intermixed with customary law and the Roman Dutch law. Before the Dutch colonization in the sixteenth century, indigenous kingdoms ruled the archipelago independently with their own custom laws, known as adat. Foreign influences from India, China and Arab have not only affected the culture, but also weighed in the customary adat laws. Aceh in Sumatra, for instances, observes their own sharia law, while Toraja ethnic group in Sulawesi are still following their animistic customary law.