The major Islamic organizations that have appeared in Indonesia in the twentieth century-Sarekat Islam, Muhammadijah, Nahdlatul Ulama and Masjumi-have all been representatives of the group that emphasizes traditional Middle Eastern Islamic beliefs and practices. All have been concerned with the primacy of Islamic law, even though their concepts of just what constituted that law were vague and different from one another. All have maintained that religious values are so important that the state should be responsible for assuring the adoption of such values throughout Indonesian society, although again there has been no common concept of what these values actually are or just what the state was to do about them. All have been convinced that the traditional Islamic values are correct and that all of Indonesian society should come to accept this premise, but there has been a wide variety of interpretations as to just how these traditional values should be implemented in contemporary Indonesian life. The value of the Persatuan Islam as a topic for scholarly research lies not in its organization, for it was small and loosely knit, nor does it lie in its participation in Indonesian political life over the past forty-five years, for its activity was incidental and peripheral to the mainstream of political developments. Although its role in religious education made some impact on Indonesian Muslims, it has been far less influential than several other organizations. In the same manner, its press has been influential at times but has never attained the stature and readership among Indonesians accorded the publications of several other Muslim organizations. Rather, the Persatuan Islam is important because it has attempted to define for Indonesian society just what it is that constitutes Islam, what the basic principles of that religion are, and what constitutes proper religious behavior for Muslims. In this presentation, the Persatuan Islam has avoided vague concepts and generalizations-somewhat unusual in Indonesia-and has dealt with the details and substance of religious behavior in Indonesia. Its members have propounded very definite views toward traditional Indonesian culture, toward developments occurring in the twentieth century, toward "Western" culture and toward traditional Muslim religious thought and practices.