Indonesia has a long history of Islam developing dynamically within its multicultural society. The development of Islam in Indonesia can be broken into several eras: 1) The pioneers of Islam and three popular theories about its introduction; 2) The colonial and pre-independence era where Islam faced threats from government policy; 3) The post-independence and New Order era where Muslim people got organized and Islamic legal products developed; 4) The modern and Reformation era bringing religious freedom and consideration of Islam in politics. Today, Islam plays an important role in overcoming multiculturalism through religious enthusiasm, different Islamic schools of thought, and three targets of harmonization: Islamic education, Islamic parties, and religious harmonization programs.