The two largest Islamic organizations in Indonesia

MuhammadiyahOn November 18, 1912, Ahmad Dahlan— a court official of the kraton of Yogyakarta[2] and an educated Muslim scholar from Mecca—established Muhammadiyah in Yogyakarta. There were a number of motives behind the establishment of this movement. Among the important ones are the backwardness of Muslim society and the penetration of Christianity. Ahmad Dahlan, much influenced by Egyptian reformist Muhammad 'Abduh, considered modernization and purification of religion from syncretic practices were very vital in reforming this religion. Therefore, since its beginning Muhammadiyah has been very concerned with maintaining tawhid, and refining monotheism in society.
As The leading national "modernist" social organization, Muhammadiyah, has branches throughout the country and approximately 30 million followers.  Muhammadiyah runs mosques, prayer houses, clinics, orphanages, poorhouses, schools, public libraries, and universities. On February 9, Muhammadiyah's central board and provincial chiefs agreed to endorse the presidential campaign of a former Muhammadiyah chairman. This marked the organization's first formal foray into partisan politics and generated controversy among members.
Nahdlatul Ulama (NU)
The NU was established on January 31, 1926 as a reaction to the modernist Muhammadiyah organization. In 1965, the group took sides with the General Suharto-led army and was heavily involved in the mass killings of Indonesian communists. However, the NU later began to oppose Suharto's regime. In 1984, Abdurrahman Wahid, the grandson of NU founder Hasyim Asy'ari, inherited the leadership from his father, and was later elected President of Indonesia in 1999. He formally apologized for NU's involvement in the events of 1965. He also stated that "Nadhatul Ulama (NU) is like Shiite minus Imamah; similarly Shiite is NU plus Imamah." There have been too many similarities between the two, such as the position and role of kyai. The main contrast between them is that in NU, the concept is visible in the form of accepted culture, while in Shia, it takes the form of theology.[1]
as the largest "traditionalist" social organization, focuses on many of the same activities as Muhammadiyah and indirectly operates a majority of the country's Islamic boarding schools. Claiming approximately 40 million followers, NU is the country's largest organization and perhaps the world's largest Islamic group. Founded in 1926, NU has a nationwide presence but remains strongest in rural Java. The Islam of many NU followers has heavy infusions of Javanese culture, and followers tend to reject a literal or dogmatic interpretation of Islamic doctrine. Many NU followers give great deference to the views, interpretations, and instructions of senior NU religious figures, alternately called "Kyais" or "Ulama." The organization has long advocated religious moderation and communal harmony.

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