This review develops a configurational account of the relationship between religion and transnationalism by addressing a specific analytical limitation in the existing literature: its tendency to oscillate between substantializing religious traditions as already constituted entities that move across borders and segmenting transnational religion into disconnected domains such as networks, migrant communities, diasporic identities, institutions, political mobilization, digital mediation, social support, or pilgrimage. While these approaches have generated substantial empirical insight, they leave undertheorized the relational formation through which religious authority, practice, identity, material circulation, symbolic boundary-making, institutional organization, and mediated presence are assembled and made socially effective across multiple scales. To clarify this problem, the review reconstructs scholarship on religion and transnationalism through five major thematic domains: transnational religious networks, religious identity in transnational contexts, religion as a catalyst of transnationalism, the embedding of religion in transnational social practices, and distinctive forms of transnational religion. This reconstruction shows that transnational religious phenomena are inadequately understood as the spatial extension of pre-given traditions, as residual expressions of ethnicity or migration, or as discrete networks, movements, institutions, or diasporic communities. They are better grasped as historically contingent and relationally ordered formations whose temporary coherence is produced through the interaction of actors, authorities, practices, discourses, infrastructures, legal-regulatory environments, memories, obligations, and material flows. Building on the concept of social configuration, the review therefore proposes transnational religious configurations as a more precise unit of analysis for studying how the religious and the transnational are mutually constituted rather than externally connected. It defines such configurations as historically specific formations in which religious categories, institutions, practices, authorities, material resources, symbolic boundaries, and cross-border conditions of possibility are articulated across local, national, transnational, and global scales. The review operationalizes this approach through three analytical levels—conditions of possibility, construction and characteristics, and social realities and consequences—and illustrates its explanatory purchase by examining a new phenomenon within the contemporary transnational revival of Shi‘i Islam.