Globalization is a key challenge facing health policy-makers. A significant aspect of this is direct trade in health services, a result of the rise of transnational corporations, challenges in health care financing, porous borders and improved technology creating the scope for increased 'foreign direct investment' (FDI) in health care. This has gathered momentum with the General Agreement on Trade in Services (GATS), which aims to further liberalize trade in services, and within which FDI has been noted as perhaps the most critical area for trade negotiation. Given the rapid development of this area, there are little empirical data. This paper therefore seeks to provide the first comprehensive and systematic review of evidence concerning FDI and health services. This process included electronic bibliographic database searches, website searches and correspondence with experts in the area of trade in health services, from which 76 papers, books and reports were reviewed. Perhaps due to the rapid developments in this area, most of the literature is speculative, polarized between those arguing for the benefits of liberalization and those arguing against. However, there seem to be three issues which emerge as of most importance: (i) the extent to which a national health system is commercialized per se is of more significance than whether investment in it is foreign or domestic; (ii) the national regulatory environment and its 'strength' will significantly determine the economic and health impact of FDI, the effectiveness of safeguard measures, and the stability of GATS commitments; and (iii) any negotiations will depend upon parties having a common understanding of what is being negotiated, and the interpretation of key definitions is thus critical. Each of these issues is explored in some depth, with the overall conclusion that countries should take a step back and first think through the risks and benefits of commercialization of their health sector, rather than being sidetracked in to considering the level of foreign investment.