Since independence, Indonesia has gradually formalized a system of religious pluralism that grants equal recognition, rights, and protections to multiple religious groups. And Indonesian Muslims--who account for some 88 percent of the population--are often described as more tolerant of religious diversity than their co-religionists elsewhere. Yet in the eighteen years since Indonesia's transition to democracy, religious pluralism has come under pressure from a series of developments that affect Muslims and non-Muslims alike. These include campaigns to assert the primacy of Islam relative to other faiths, "purify" the beliefs and practices of Indonesian Muslims, and Islamize the state. They also include the increasing adoption of pious dress by Muslims, which has made religious identities--and religious divisions--visible in a way they never were under Sukarno or Suharto. These developments suggest that intertwined processes of democratization, decentralization, and sociocultural Islamization are recontextualizing questions of how religious pluralism is institutionalized and practiced in Indonesia. This dissertation explores different manifestations of pressure on religious pluralism in post-transition Indonesia. After tracing the historical development of religious pluralism in Indonesia, I examine pressures emerging from and manifesting themselves in legislative challenges to religious pluralism at the level of the state; localized protests against the building of new churches; and the adoption of pious dress in everyday life. I argue that democratization, decentralization, and sociocultural Islamization are neither reinforcing nor dismantling Indonesia's system of religious pluralism. Rather, they are producing sharp and growing disparities in how pluralism is institutionalized and practiced: disparities across regions, localities, and groups. By eschewing the ideologically charged question of whether Islam is compatible with religious pluralism in favor of an empirical investigation of the ways Islamization generates multiple and distinctive pressures on religious pluralism, I endeavor to provide a nuanced portrait of a society struggling to reconcile heightened Islamic claims-making with long-standing traditions of pluralism.