Recent work in cultural sociology has noted the importance of boundaries for understanding intergroup relations. Within the sociology of religion, this has manifested in research into interreligious conflict and cooperation. However, the current literature often assumes that boundaries have fixed qualities and generate clear consequences for group interaction. In this article, we draw on two data sets, comprising interviews and ethnographic data on ten different religious groups from a variety of faith traditions, to demonstrate that cultural resources, including religious beliefs, (...) may be used to assess the meaning and saliency of boundaries. Particular qualities of boundaries shape how social actors understand and interpret group difference, suggesting that boundaries themselves are a site of struggle. Finally, we use the concept of relational principles as a heuristic device to organize and understand the different ways that our subjects manage and assess competing boundaries. (shrink)