It is difficult to overstate the importance of the concept sovereignty for international relations (IR). And yet, understanding the historical emergence of sovereignty in international relations has long been curtailed by the all-encompassing myth of the Peace of Westphalia. While criticism of this myth has opened space for further historical inquiry in recent years, it has also raised important questions of historical interpretation and methodology relevant to IR, as applying our current conceptual framework to distant historical cases is far from unproblematic. Central among these questions is the when, what, and how of sovereignty: from when can we use “sovereignty” to analyze international politics and for which polities? Can sovereignty be used when the actors themselves did not have recourse to the terminology? And what about polities that do not have recourse to the term at all? What are the theoretical implications of applying the concept of sovereignty to early polities? From different theoretical and methodological perspectives, the contributions in this forum shed light on these questions of sovereignty and how to treat the concept analytically when applied to a period or place when/where the term did not exist as such. In doing so, this forum makes the case for a sensitivity to the historical dimension of our arguments about sovereignty—and, by extension, international relations past and present—as this holds the key to the types of claims we can make about the polities of the world and their relations.