This chapter considers three concepts—state, territory, sovereignty—that are fundamental not only to the intersection of History and International Relations (IR) but also to IR theoretical debates. We track how the literature on these concepts has changed over time and discuss broad critiques and avenues for future research. We argue that state, territory, and sovereignty need to be studied as analytically distinct yet interrelated outcomes and processes. Key challenges for historical IR scholarship include overcoming a Eurocentric bias inherent in these concepts, how to apply contemporary concepts to earlier historical periods, and how—and whether—to draw lessons from history for contemporary politics. Finally, historical IR scholars could pay more attention to the important yet largely unexplored material dimensions of state, territory, and sovereignty.