This dissertation investigates the social construction of Islamic orthodoxy as a form of boundary maintenance within Muslim milieus in contemporary Sweden. It delves into the dynamics of intra-Islamic diversity, examining how different Muslim groups perceive and define what constitutes “correct” Islamic faith and practice in contrast to what they consider “incorrect”. By employing positioning theory, the study explores how perceptions of both selves and others influence discourses on Islamic orthodoxy, particularly through notions of religious duties, rights, and obligations. The study is rooted in ethnographic fieldwork conducted in a multicultural suburb where different Islamic congregations coexist. The study investigates the interplay of local, national, and global dynamics, highlighting how these factors impact religious identities and positioning around orthodoxy. Through participant observation, in-depth interviews, and content analysis of sermons and lectures, the study reveals the dialectical nature of how orthodoxy is constructed. It demonstrates how perceptions of “other” Muslims, whether within the same community or across different denominations, are significant for reinforcing one’s own religious identity and practices. The findings of this dissertation highlight aspects of how local Islamic congregations and individual Muslims navigate the multifaceted challenges posed by Sweden’s multicultural and secular society. Among other things, they are shown to actively negotiate their place within this culturally diverse environment, balancing the pressures of integration with the desire to maintain religious integrity—while positioning both their own and other views on orthodoxy in relation to these contemporary issues.