Inspired by recent work in evolutionary, developmental, and systems biology, Systems, Relations, and the Structures of International Societies sketches a robust conception of systems that grounds a new conception of levels (of organization, not merely analysis). Understanding international systems as multi-level multi-actor complex adaptive systems allows explanations of important features of the world that are inaccessible to dominant causal and rationalist explanatory strategies. It also develops a comprehensive critique of IR's dominant conception of systems and structures (narrow, rigid, and unfruitful); presents a novel conception of the interrelationship of the social production of continuities and the social production of change; and sketches models of spatio-political structure that cast new light on the development of international systems, including a distinctive account of the nature of globalization.