What are levels of analysis and what do they contribute to international relations theory?

The objective of this article is to clarify the significance and usefulness of levels of analysis, a central IR concept, but one often used unproblematically. I argue that a level of analysis should be defined as a social structure that is examined for its effects on another social structure, or on the same social structure. Therefore, levels of analysis are also relational, meaning that one is defined, in part, in terms of its associated unit of analysis. Because this definition conceptualizes levels of analysis as methodological tools rather than ontological postulates, it is consistent with a wide range of positions on the agent-structure debate. More specifically, I show that the methodological issue of which levels of analysis a researcher employs is separate from the ontological issue of whether the theoretical lens is atomistic (reductionist) or holistic at any given level. One implication of this definition is that researchers need not view their ontological commitments as overly methodologically constraining. This article also addresses some questions raised by this conceptualization, among them the possibility of multiple social structures existing at a single level.