“Human nature” is not a notion that has originated from theories of world politics. On the contrary, it represents one of the oldest points of reference in various cultural traditions of thought. An aspect, however, that makes the current status of the human in international relations (IR) interesting is the fact that since the 1980s, the discipline has undergone a rigorous and critical examination of its core terminologies. Above all, this effort has led scholars to become aware of the concurrent appropriations of their terms: once as scientific concepts and once as ontological facts. However, while various aspects of the human have always found their way into the theorization of world politics, so far the actual impact of the equally diverse “models of man” on the latter has hardly been subjected to systematic consideration. Observing “human nature” not only as a “naturally given fact” but also as an observational concept connects IR with the broader literatures on how the (political) world may be interpreted and analyzed. The proposition to begin a reappraisal of “human nature’s” framing effects on the basis of the distinction of anthropological and post-anthropological approaches (Human Beings in International Relations. Cambridge, UK: Cambridge University Press, 2015) calls upon IR scholars to appreciate what happens when they study world politics through a lens that either places the human at the center of its observations or one that opts to decenter it to different extents. A reflection on the distinction of an international political anthropology and an international political post-anthropology as a starting point for theory building then not only draws attention to what is included and excluded in regard to the human when studying world politics. It moreover exposes how different views on the (post)human come to shape different theoretical architectures. What is more, it also reveals that such foundations do not run parallel to the classical IR heuristic of distinct paradigms. A closer look at their post-human foundations then shows how much these schools of thought, once conceived as highly coherent, have now been differentiated internally. The said absence of a systematic debate on the status of the human in the IR theories also poses a challenge to this article. Not only is the human still rarely reflected upon as a theoretical core concept; at the same time, parallel debates exist that are guided less by theoretical frameworks but rather by the problems that arise from specific ideas about the post-human. In this sense, this article also pursues a dual strategy: on the one hand, the listing either of obvious or subtle uses of post-human views by various theoretical traditions, and on the other hand, the identification of specific core problems that have formed in the wake of specific angles on the post-human. Since inquiries into the post-human also include an intersection of IR theories with other scientific literatures, the article also features text references that will help readers find their way into the state of the art of those important adjacent debates.