IR typically understands levels as levels of analysis that produce analytic/reductionist (rather than systemic/relational) explanations. Causes, separated by levels, are looked at as independent variables understood as distinct sources of explanation. Systemic explanations rely instead on related elements and levels of organization that are (understood to be) in the world (not just convenient epistemic devices). Systems approaches claim that parts on one level are organized into higher-level wholes that are themselves structured parts of still-higher-level wholes. (For example, subatomic particles, atoms, elements, chemical compounds.) The chapter concludes by examining the implications of a levels of organization framing for four important metatheoretical issues: micro–macro relations, the agent–structure problem, the natures of individual human beings and social groups, and the natures of individual and group identities.