From a critical realist perspective, this book examines the manner and the extent to which religion is shaped by modernity. With a focus on Poland, one of the most monolithic and religiously active Catholic societies in the world - but which has undergone periods of intense transformation in its recent history - the author explores the transformations that have affected Catholicism from a position of reflexivity. Viewing Catholicism as a system of ideas elaborated by tradition, the author considers the relationship between human subjectivity and social structure by examining the shift from traditional religious practice to modern religious observance, particularly in an era of migration in which many Polish Catholics have relocated to western European countries, with profound changes in their religious outlook. Presenting a new approach to understanding religious change from the perspective of religious reflexivity, Polish Catholicism between Tradition and Migration will appeal to scholars across the social sciences with interests in religion, research methods, social change and critical realist thought.