We advance nonprofit scholarship by using the conceptual framework of policy fields to examine differences across nonprofit fields of activity. We focus on the structure of relationships among four sectors (government, nonprofit, market, informal) and how relationships differ across policy fields (here health, human services, education, arts and culture, and religion). The fields differ notably in the economic share that each sector holds and the functional division of labor among the sectors. Systemic differences also exist in how the nonprofit sector interacts with the government, market, and informal sectors. The policy fields themselves operate within national contexts of distinctive economic and political configurations. The framework explores how government-nonprofit relationships differ across policy fields, the factors responsible for this variation, and offers predictive capacity to generate hypotheses and research designs for additional research. We provide insights on how nonprofit organizations differ in key sub-fields with direct relevance for policy and practice.