Indonesia is about 87% Muslim, making it the country with the largest Muslim population on earth — roughly 240 million people, more than the entire Arab world combined. It is not, however, an Islamic state. Indonesia officially recognises six religions, requires citizens to hold one of them, and is founded on a state philosophy that mandates belief in God without specifying which.
The Six Religions on Your Identity Card
Indonesian national identity cards, the KTP, carry a religion field, and until recently it could hold only one of six entries: Islam, Protestantism, Catholicism, Hinduism, Buddhism or Confucianism. Protestantism and Catholicism are listed separately, which is why Indonesia is sometimes described as recognising six religions and sometimes five.
| Religion | Share |
|---|---|
| Islam | ~87% |
| Protestantism | ~7% |
| Catholicism | ~3% |
| Hinduism | ~1.7% |
| Buddhism | ~0.7% |
| Confucianism | ~0.03% |
The field is not cosmetic. It has historically affected marriage registration, burial arrangements, schooling and employment, and leaving it blank was not an option — which meant adherents of Indonesia's many indigenous faiths had to nominate something they did not believe.
Pancasila Requires a God but Names None
Indonesia's founding philosophy, Pancasila, opens with Ketuhanan Yang Maha Esa — belief in one almighty God. It is the first of five principles and it does the country's central balancing act: it commits the state to theism while refusing to establish any particular religion.
The compromise was deliberate and hard-won. The original Jakarta Charter of June 1945 included a clause obliging Muslims to follow sharia; it was struck out the day before independence was proclaimed, largely to keep the Christian-majority eastern territories inside the new republic. Those seven deleted words have been argued over ever since.
The practical consequence is a state that is neither secular nor Islamic. Atheism sits awkwardly with the first principle, and Indonesia has prosecuted people for declaring it.
Two Organisations Larger Than Most Countries
Indonesian Islam is shaped less by the state than by two mass organisations, both of which predate independence and are the largest Muslim civil society bodies in the world.
Nahdlatul Ulama, founded in 1926, claims something in the order of 40 million members and is rooted in traditionalist rural Java, with a network of pesantren boarding schools. Muhammadiyah, founded in 1912, claims around 30 million, is modernist and urban, and runs an enormous infrastructure of schools, universities and hospitals — including institutions that serve non-Muslims.
Between them they anchor a broadly moderate mainstream, and their leaders have repeatedly been decisive in national politics. Abdurrahman Wahid, who led NU for fifteen years, became president in 1999.
Aceh Is the Only Province Under Sharia
One province operates under Islamic law, and only one. Aceh, on the northern tip of Sumatra, received special autonomy in 2001 as part of the settlement of a long separatist conflict, and that autonomy included the right to implement sharia.
In practice this means religious police, dress regulations, prohibition of alcohol and gambling, and corporal punishment — public caning — for offences including adultery, gambling and same-sex relations. Non-Muslims in Aceh can in some circumstances elect to be tried under it.
The 2004 Indian Ocean tsunami, which killed well over 100,000 people in Aceh alone, both devastated the province and accelerated the peace process that confirmed the arrangement. Nothing comparable applies anywhere else in Indonesia.
Bali Is Hindu, and Not Quite Like India's
Bali is the great exception in the archipelago: roughly 87% Hindu in a country that is 87% Muslim, an inversion that makes it feel like a different country to visitors and, in some respects, is.
Balinese Hinduism, formally Agama Hindu Dharma, is a distinct synthesis of Shaivism, Buddhism and pre-existing Austronesian ancestor and spirit worship. It emphasises ritual, offerings and community temple obligations more than the philosophical traditions dominant in India, and it has its own festival calendar — Nyepi, the day of silence, shuts the entire island down, including the airport, for 24 hours.
The island is the last remnant of a Hindu-Buddhist order that governed Java for centuries. When the Majapahit empire fell to Islam around 1500, much of its priestly and aristocratic class relocated east to Bali.
Borobudur, Prambanan and the Buddhist-Hindu Centuries
Central Java holds the two largest monuments of that earlier order, built within decades of each other in the ninth century and now both UNESCO World Heritage sites.
Borobudur is the largest Buddhist temple in the world: a stepped stone mandala of nine platforms carrying over 2,600 relief panels and 500-plus Buddha statues, abandoned around the fourteenth century and lost under volcanic ash and jungle until the nineteenth. Prambanan, some 40 km away, is the largest Hindu temple compound in Indonesia, dedicated to the Trimurti.
That two of the world's great Buddhist and Hindu monuments stand in what is now the most populous Muslim-majority country is the sharpest possible illustration of how completely Indonesia's religious composition has changed — and how peacefully the change largely happened, spread by trade and Sufi missionaries rather than conquest.
Christianity in the East
Indonesia's roughly 10% Christian population is not evenly spread; it is concentrated at the geographic edges, and in several provinces it is the majority.
East Nusa Tenggara is heavily Catholic, a legacy of Portuguese presence. North Sulawesi, Papua and West Papua are strongly Protestant, largely through Dutch missionary activity. The Batak of North Sumatra were converted by German Lutheran missionaries in the nineteenth century and now form one of the largest Protestant communities in Asia.
This distribution matters politically. It is why the Jakarta Charter's sharia clause was removed in 1945, why proposals to reinstate it have consistently failed, and why religious tension in Indonesia has often been sharpest in the places where the communities are most evenly balanced, such as Maluku and Poso in the early 2000s.
How Islam Arrived Without an Army
Indonesia's conversion is unusual among large Muslim countries in that no caliphate ever conquered it. Islam arrived with Gujarati, Persian and Arab traders working the spice routes from around the thirteenth century, and spread through port cities first — Samudera Pasai in northern Sumatra is the earliest attested Muslim polity, from the late 1200s.
The traditional account credits nine saints, the Wali Songo, with converting Java in the fifteenth and sixteenth centuries. What is historically clear is that they worked by accommodation rather than confrontation: Sunan Kalijaga is remembered for using wayang shadow puppetry, an existing Hindu-Javanese art form, to teach Islamic ideas, and Javanese mosques were built in the tiered style of earlier Hindu-Buddhist meru towers rather than in Middle Eastern forms.
That inheritance is still visible. Javanese Islam absorbed a great deal of what preceded it, which is why selamatan communal meals, veneration of saints' graves and elements of the Hindu-derived calendar persist alongside orthodox practice — and why reformist movements have spent a century arguing about whether they should.
Istiqlal and the Cathedral Across the Road
Jakarta's Istiqlal Mosque is the largest mosque in Southeast Asia, with capacity for over 200,000 people. Two details about it are quietly deliberate.
Sukarno commissioned it after independence and chose the winning design from an open competition; the architect, Frederich Silaban, was a Christian Batak. And it stands directly opposite the Catholic Cathedral of Our Lady of the Assumption, its site selected for exactly that adjacency. The two share parking during each other's major festivals, and in 2020 a pedestrian tunnel was built between them.
The symbolism is officially cultivated, and it is fair to note that symbolism is easier than practice — permits for building churches in Muslim-majority districts remain a genuine and long-running source of friction, governed by a 2006 joint ministerial decree requiring local approval that is often withheld.
The Faiths That Were Not Allowed on the List
Indonesia has hundreds of indigenous belief systems — collectively aliran kepercayaan — including Kejawèn in Java, Sunda Wiwitan among the Baduy, Kaharingan in Kalimantan and Marapu on Sumba. For decades they had no recognition, and their adherents had to register as one of the six.
That changed in November 2017, when the Constitutional Court ruled that citizens could record Kepercayaan — belief — on the identity card. It was a significant decision affecting an estimated 10 to 12 million people, though implementation has been uneven and the underlying pressure to affiliate has not disappeared.
Confucianism illustrates how contingent the list is. It was recognised in 1965, effectively banned under Suharto's New Order as part of a broader suppression of Chinese Indonesian culture, and restored only in 2000 under President Wahid.
Blasphemy Law and Where the Balance Strains
The framework's limits show most clearly in its blasphemy provisions. Article 156a of the criminal code criminalises expressing hostility towards a recognised religion, and prosecutions have increased markedly since the 2000s.
The most prominent case was that of Basuki Tjahaja Purnama, the Christian governor of Jakarta known as Ahok, convicted in May 2017 and sentenced to two years after mass demonstrations over remarks he made about a Quranic verse during a campaign appearance. Minority Muslim groups have also been targets: Ahmadiyya communities have faced restrictions and violence, and Shia minorities have been displaced.
Indonesia is therefore neither the pluralist model nor the hardline state it is alternately described as. It is worth setting against India, the other enormous Asian democracy built on religious plurality, which took the opposite constitutional route and recognises no official list of faiths. It is a country that built an unusual constitutional compromise in 1945, has largely held to it for eighty years, and argues continuously about where its edges are. The pattern of six recognised faiths and a shared national calendar also explains the shape of Indonesia's public holidays, which rotate through all six.