The notion that the spread of Christianity should be primarily credited to intentional, organized missionary efforts has long been predominant in the study of the religion. Migration often finds a more prominent role in historical treatments of Christianity’s expansion after the mid-nineteenth century—given technological advances and other factors that encouraged widespread dislocations of people groups. The changes brought by modern European colonialism and the Reformation have also captured, for good reason, the imagination of scholars who have paid attention to how cross-cultural encounters and migration have helped shape Christianity after the sixteenth century. Coherent and concise assessments of the role of migration in the expansion and diversification of Christianity around the world during the centuries that preceded the Reformation, however, are less common. Although a few scholarly volumes have addressed the development of Christianity beyond the West since its beginnings, Jehu J. Hanciles’s Migration and the Making of Global Christianity fills an important gap in the scholarly literature by addressing the importance of migration in this broader dynamic.Hanciles provides an ambitious sociohistorical study of the first fifteen hundred years of Christianity in which migrants take center stage as agents of Christianity’s expansion and diversification. Hanciles’s choices for showing the continuing significance of migration in global Christianity are broad in scope and geography. From the Roman Empire to Persia and from medieval Europe to Asia and the Mongol Empire, Hanciles narrates, analyzes, and interprets critical moments in the history of Christianity in which migration took center stage not only in Christianity’s spread but also in its theological development. Throughout the history of Christianity, migration was, Hanciles claims correctly, “often a theologizing experience” (118). This migration-informed theologizing was widespread as different people tried to make sense of new social, cultural, and linguistic contexts at different times. Examples abound; they include the discourse of exile in the Hebrew Bible, the incorporation of non-Jewish Christians in the New Testament, numerous Christian leaders who incorporated in their theologies aspects of the transnational lives they lived, and migrant experiences on the ground that influenced people to appropriate and translate top-down Christian messages in different ways.Despite this book’s many historical contributions, Migration and the Making of Global Christianity is not an encyclopedic account of one fact after another. As a matter of fact, the primary contributions of Hanciles’s work may reside in his methodological decisions and outlook. At the heart of Hanciles’s project lies the goal of decentering missionaries as singular, primary agents of Christian expansion and introducing migrant experiences as key to the development of Christian history and theology. He does that without romanticizing migrant encounters and experiences—intra-Christian and otherwise—as necessarily benign. Migration and the Making of Global Christianity reminds us that migration is intertwined with the development of Christianity, often despite or because of uncomfortable phenomena created by particular historical contexts. Diverse contextual challenges encountered by migrant groups and individuals—such as violence, economic struggle, underdeveloped cultural repertoires, linguistic limitations, misunderstandings, power differentials, and narrow theological convictions—were crucial for Christianity’s expansion, diversification, and theological development. By decentering missionaries as primary agents of expansion, Hanciles also questions the sufficiency of what he calls “the empire argument” that traces a strong relationship between political and religious development. For him, “the empire argument distorts historical understanding not only because it places disproportionate emphasis on formal structures, official agency, and state resources that played a minimal role in Christian expansion but also because it minimizes the importance of the recipient societies and the agency of potential converts” (415). Although Hanciles’s take on empire might be read as potentially lacking a robust account of empire in all its forms, Migration and the Making of Global Christianity does engage the issue of conversion and religious appropriation in ways that help qualify arguments that reduce Christian expansion to a function of imperialism.To address sufficiently the different dynamics involved, Migration and the Making of Global Christianity is conversant with several disciplines such as theology, migration studies, and sociology. Hanciles’s approach is, therefore, explicitly historical in general and sociohistorical in particular, but it has strong interdisciplinary elements. Historians judging by the standards of traditional historical practice will notice that Hanciles relies overwhelmingly on secondary accounts. His historical interpretation is often layered on top of other interpretations rather than resulting from vigorous engagement with primary sources. This is understandable considering the ambitious conceptual, historical, chronological, and geographical scope of the book. Yet, Hanciles’s command of sources in different fields is impressive. Migration and the Making of Global Christianity should be read by historians, theologians, and sociologists for its contributions in showing that migration is a core element in the expansion, diversification, and theological development of Christianity. Hanciles’s work is indispensable reading for scholars and practitioners interested in migration studies and world Christianity, and may soon be considered necessary reading in mission studies.