This chapter examines the nature, availability and shortcomings of direct foreign investment (DFI) data collected within the United States and internationally. Despite the importance of DFI to a country's balance of payments and the implications for factors such as trade, employment and transfer of technology, national data on DFI are weak. The quality of international data on DFI is extremely weak in many respects. Data related to balance of payments are collected primarily for inclusion in the US balance of payments accounts and for calculating the international investment position of the United States. Attempts to conduct serious empirical research in the emerging area of intra-industry DFI are likely to confront the same, and perhaps even more severe, data problems. Differences in reporting systems result in potentially significant differences in the composition of the DFI data. The company survey technique generally permits a more complete estimation of DFI than does cash-flow reporting.