Islam is the majority religion in Indonesia. The country has a larger Muslim population than any other country in the world, with approximately 202.9 million identified as Muslim (88.2% of the total population). Despite being the country in the world with the most Muslims, Indonesia is a secular state.

Majority adhere to the Sunni Muslim tradition mainly of the Shafi`i madhab, although some follow other branches of non-Sunni Islam, predominanently Shia and Ahmadiyya. Shia number around 1 million. Whereas Ahmadiyya number around 0.5 million. In general, the Muslim community can be categorized in terms of two orientations: "modernists," who closely adhere to orthodox theology while embracing modern learning; and "traditionalists," who tend to follow the interpretations of local religious leaders (predominantly in Java) and religious teachers at Islamic boarding schools.

When Indonesia declared independence in 1945, it became the second largest Muslim-majority nation in the world; following the separation of Bangladesh from Pakistan in 1971, it emerged as the most populous Muslim country in the world.

The Istiqlal Mosque in Jakarta is the largest mosque in the country, and the largest mosque in south east Asia.

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