Abstract Consensus on the concept of foreign direct investment (FDI) has sparked an enormous body of research that confirms the importance of separating FDI and its politics from other forms of international economy activity. At the same time, international political economy research on FDI is in danger of becoming a victim of its own success: by too readily accepting the parameters of “F,” “D,” and “I,” we risk undervaluing high-priority research agendas that push conceptual boundaries. As evidence, this chapter highlights gains made by probing the “F” in FDI—by disaggregating national origins; separating foreign state or private owners; and considering “F” in the context of its domestic counterparts. Recognizing the huge progress made due to de facto agreement on what constitutes FDI, scholars in all IPE research traditions would do well to prioritize research questions that critically engage with the concept.