Book excerpt: The role of migration for Christianity as a world religion during the last two centuries has drawn considerable attention from scholars in different fields. The main issue this book seeks to address is the question whether and to what extent migration and diaspora formation should be considered as elements of a new historiography of global Christianity, including the reflection upon earlier epochs. By focusing on migration and diaspora, the emerging map of Christianity will include the dimension of movement and interaction between actors in different regions, providing a more comprehensive ‘map of agency’ of individuals and groups previously regarded as passive. Furthermore, local histories will become parts of a broader picture and historiography might correlate both local and transregional perspectives in a balanced manner. Behind this approach lies the desire to broaden the perspective of Ecclesiastical History – and religious history in general – in a more systematic manner by questioning the traditional criteria of selection. This might help us to recover previously lost actors and forgotten dynamics.